Whether your order has been cancelled or you've received less-than-impressive groceries, the nation's supermarkets have policies on how long you can expect to wait before getting your money back - but some shoppers have reported waiting weeks or even months for their refunds.
Which? contacted dozens of shoppers who left complaints on supermarkets' social media pages stating they had been left without food or the means to pay bills as a result of overdue refunds.
Here, we share some of their stories and explain what you can do if you experience an overdue refund yourself.
While we came across stories of overdue refunds from shoppers at all of the UK's major supermarkets, those who were happy to be included in this article were Tesco and Sainsbury's customers.
Multiple Sainsbury's shoppers have waited weeks longer than the supermarket's five-working-day refund window to get their money back. One customer was without his money for around three months.
The shopper, from Newcastle-upon-Tyne, discovered their click-and-collect order did not include everything they'd paid for. They only received their money back after sending an email to Sainsbury's executive office.
Another shopper waited around six weeks to get her money returned after Sainsbury's cancelled her delivery worth close to £90 in January.
Elisabeth Pearson from Glanamman in Carmarthenshire, Wales called Sainsbury's four times to ask how long she'd be waiting, and was told it could be up to 10 days before she received her money back.
Elisabeth had to borrow money to cover bills because of the incident. 'The inconvenience was terrible. I'm on benefits and budget carefully,' she said. 'Sainsbury's wouldn't have tolerated it the other way around.'
Sainsbury's issued a £20 voucher in light of the delay.
A primary school employee was left without the cash they were owed from Sainsbury's for around a month.
The shopper placed a click-and-collect order for the school's Breakfast and After School Clubs and rejected three of the item substitutions, which were worth £33.26.
When they hadn't received a refund for those items a few days later, the customer called Sainsbury's about the issue. Sainsbury's then asked the shopper to send screenshots of their bank account to prove they hadn't already received the funds. The shopper informed the customer service team member they were unhappy to do this, but was told that unless they did so, Sainsbury's would not return their money.
They told Which? the issue had been 'extremely exhausting' to deal with.
We also heard from two other shoppers who waited 16 days to get their refunds. The first, Tan Morris from Worcestershire, had ordered food for her elderly parents, while the second lives solely on her pension and struggled to feed herself because of the delay.
Selina Kindrat Pang from Barnet, North London, meanwhile, also had to borrow money and food from family and friends when Sainsbury's took over two weeks to refund the £150 she was owed.
Selina's order was cancelled without warning, and she was issued three £50 vouchers after calling its helpline several times. But she then discovered that a technical issue on Sainsbury's website meant it did not accept vouchers worth the same value as one another.
'I then had to spend another hour calling back and having it rectified before the refund was reissued as £49, £50 and £51 tokens,' she said.
Selina said what happened made her feel 'let down' by Sainsbury's, adding that she no longer shops there on principle. Sainsbury's sent Selina a £20 voucher as a 'goodwill gesture'.
Didge Mears from Devon placed an order with Sainsbury's that never turned up. The supermarket assured Didge in an email that he would not be charged for the food, but £98.16 was debited from his bank account the following day.
Didge called Sainsbury's a total of five times to try and get his refund sorted. He told Which? that Sainsbury's refund team informed him they had 'no idea' how long it would be until he got his money back due to the large number of customer calls they were getting.
'Sainsbury's is quick enough to take customers' money, but clearly not respectful enough to promptly return it when they make a mistake,' Didge said.
'People need to be cautious, especially those on low incomes who cannot afford for errors like this to happen. This situation is unacceptable, and Sainsbury's should be held accountable for its tardy behaviour.'
When we put our findings to Sainsbury's, it told Which?: 'We fulfil tens of millions of groceries online orders every year and are committed to offering the best possible service. The case studies Which? has shared do not represent what the vast majority of our customers experience.'
The spokesperson said that there are some 'rare occasions where a store responsible for the cancellation may be unable to generate the refund. In these cases it is passed to our careline team to resolve, which may cause a slight delay. Any delay to a customer receiving their refund is extremely rare and we'll put this right as soon as it is brought to our attention.'
Which? will continue to monitor the situation.
Which? also heard from Tesco shoppers who have been left disappointed by a long wait to get their money back.
Neo Dark from Kent waited six working days to get his money back from Tesco for his £144.44 order.
Neo Dark, from Kent, was informed via text message that his Tesco delivery driver was running late. He was then told an hour later that his delivery had been cancelled due to 'unexpected roadworks and a large number of orders'. He was given a £10 e-voucher for the inconvenience alongside the money he was owed - but not until six working days later.
Neo, who suffers with several health conditions and relies on deliveries, told Which? he only 'considers Tesco as a last resort' to do his food shopping now.
Another shopper struggled to feed his family after he was charged twice for his £100.34-worth of shopping.
Mark Randall from the West Midlands did his usual weekly shop in June and realised he had 'very little money' left in his account the following day. He discovered Tesco had debited him £100.34 once and left another £100.34 transaction pending for over a week.
Mark told us he made several calls to Tesco's customer services line to try and rectify the problem, but was advised that he would have to wait up to 10 days for Tesco to release his money. He said Tesco did not give him an explanation as to why he'd been charged twice.
'As I'm a single parent and on a very tight budget, I didn't have enough money to get my groceries the following week,' Mark said. 'Tesco really needs to take customers' needs into consideration as not everyone can afford to have money reserved [in their] accounts.'
A spokesperson for Tesco told Which? that duplicate authorisations are very rare. It has recently put a selection of measures in place to reduce them further, including an automated system that identifies duplicates and attempts to reverse them on the same day.
The spokesperson said Tesco will only cancel online orders in exceptional circumstances, and only once it has exhausted all options.
Supermarkets each have a refund window they aim to process customers' refunds within. Here is an overview of how long you can expect to wait to get your money back from the UK's main supermarkets (links take you to our reviews of each retailer):
What can you do if you experience an overdue refund?
If you've been through a similar experience as those we've reported on, or if you do in the future, there are various steps you can take to get what you're owed.
The first is writing or emailing a letter of complaint to the retailer, outlining what has happened in as much detail as possible as well as the outcome you're looking for.
Mention the fact that makes it an implied term of the contract between a retailer and shopper that goods be as described, fit for purpose and of satisfactory quality. If this is not the case, the shop has breached its end of the contract.
It's also important to note that severely overdue refunds could mean the retailer has broken consumer law, which stipulates refunds should take place within 14 days.
You can issue a claim to the county court without any further interaction with the retailer, and state as much in your email or letter. If the retailer takes no action within a reasonable amount of time (usually up to eight weeks), however, you can.
Should the company be willing to work with the ombudsman to resolve your complaint, the aim is to reach a resolution within 10 working days. If the business is unwilling to work with the ombudsman - or a resolution that both parties are satisfied with can't be reached - the Consumer Ombudsman will advise you on what to do next.