City watchdog the Financial Conduct Authority (FCA) has announced it will investigate TSB's botched IT migration as customers endure the seventh week of disruption to their banking services.
The latest blunder has seen TSB send out letters to customers containing the name and address of other account holders.
Which? looks at the issues TSB customers are experiencing, what the regulator is doing about it and explains how to switch if you're fed up or worried about what's going to happen next.
TSB's problems started after a planned migration of 1.3 billion customer records from former owner Lloyds' IT system to one managed by current owner Sabadell on Friday 20 April.
On Tuesday 24April, TSB took its online and mobile banking service offline, but the next day customers still reported problems.
By day seven of the crisis, the bank called in IT specialists IBM to help it fix the spiralling issues.
TSB current account, credit card, mortgage and savings customers are still experiencing a variety of issues.
Some TSB credit card customers have reported failures in direct debits, meaning bill payments did not go through. TSB says customers won't incur interest for this glitch and there will be no impact on credit records.
Meanwhile, current accounts customers that have activated their 'Save the Pennies' feature are finding that transfers are still being made even when an account is overdrawn.
Earlier this week, TSB has sent out complaint acknowledgement letters containing details of other customers.
The letters that have been widely shared on Twitter show the name, address and complaint reference number of other account holders.
A TSB spokesperson told Which? Money: 'We are aware that there has been an issue with a recent acknowledgement mailing.
'This matter relates to an operational issue and we are working together with our third party supplier to ensure that this does not happen again.
'We'd like to apologise to anyone that may have been impacted.u201d
TSB CEO Paul Pester, will face MPs on the Treasury Committee for a second time on Wednesday to explain what is being done to resolve the bank's spiralling problems.
Which? Money asked the Information Commissioner's Office (ICO), which investigates data breaches, if TSB would be investigated.
An ICO spokesperson said: u201cThe ICO is continuing to make enquiries in relation to TSB and we are aware of ongoing issues. Customers who are concerned about their personal data can contact us.u201d
The Financial Conduct Authority (FCA),which regulates the banks, has confirmed it will be investigating TSB's botched IT migration.
FCA chief executive Andrew Bailey said in a letter to Treasury Committee chairwoman Nicky Morgan that the regulator would carry out a joint investigation with the Prudential Regulation Authority.
It noted: “We do not normally make this information public, but, given the level of public interest, I want to be clear that we will be conducting this work.”
Mr Bailey went on to state: “The FCA has been dissatisfied with TSB's communications with its customers and we have had concerns that TSB was not being open and transparent about the issues experienced,” adding that the bank's response “could reduce trust in TSB and in the banking sector as a whole”.
He also revealed TSB had not met requirements to refund customers as soon as possible. More than 40% of calls to TSB were abandoned or disconnected before progressing through the IVR (interactive voice recognition system) and wait times to speak to an agent had at times been longer than 30 minutes, he noted.
TSB has repeatedly said no customer will be left out of pocket as a result of the issues.
It's waiving any current account overdraft fees and interest charges, as well as any returned item fees incurred during your March, April and Maybilling periods.
In order to convince customers to stick around, the bank has also increased the interest rate on its Classic Plus account from 3% to 5% AER.
In a Which? Money Twitter poll, we asked TSB customers if they would switch in light of recent events. Perhaps unsurprisingly, 43% said yes but nearly a third (35%) said they were sticking with the bank.
Your new provider will move across all outgoing payments - including direct debits and standing orders - and any money you have left in your account within seven working days.
Crucially, switches completed through CASS come with a guarantee that you will be covered for any losses in the event of something going wrong.
Which? Money asked Bacs Payment Schemes Limited, which owns and operates the Current Account Switch Service, if TSB customers would experience any problems switching.
A spokesman said: 'We can confirm that the Current Account Switch Service continues to operate as normal and at no time has the service been unavailable to customers wishing to switch their current account.
'Bacs and the CASS participant community are working closely with TSB to complete the impacted switches, and we would also remind anyone using the service that they are protected by the Current Account Switch Guarantee in the event of an error with their switch.'