1 Complain to car hire company
Always complain to your car hire company in the first instance. You can do this verbally or in writing but make sure you keep a clear record of your complaint.
Give the car hire company a reasonable time to address your complaint and to rectify the situation, say 14 days.
If your complaint has not been resolved, you can then turn to one of a handful of organisations who have codes of conduct for members and aim to resolve disputes with customers.
2 Escalate your complaint
The European Car Rental Conciliation Service (ECRCS) has a free service to help with unresolved complaints concerning cross border vehicle rentals within Europe.
It will only deal with complaints about member companies. In June 2012 these members were Avis, Alamo, Budget, Europcar, Hertz, National and Sixt.
If you're using the ECRCS to help you get your money back, you must have booked with the car hire company direct - not through a broker or travel agent.
It will investigate to see if a car rental company has breached its code of practice. The code covers advertising, customer information, vehicle condition, pre and post-rental inspections, and billing.
The ECRCS can get refunds for charges it rules were incorrectly made by a rental company.
3 Use European Consumer Centres
You can also contact the European Consumer Centres Network, which has a free service to help resolve disputes and help you get your money back.
It will investigate if car hire companies have broken European contract law.
4 Complain to the BVRLA
For UK rentals, the British Vehicle Rental and Leasing Association (BVRLA), can help you with complaints about its members.
These include a large range of companies from big operators such as Hertz and Avis to small independents.
It operates a code of conduct and will investigate if a member has breached this. It aims to resolve disputes within 30 days.
Your complaint should be emailed to firstname.lastname@example.org or submitted in writing. The BVRLA has also produced a guide to renting a car.