I booked my summer holiday to Germany using Easyjet and the car rental service that is built into their website. This is called Easyjet Car Rentals (powered by Cartrawler).
Easyjet cancelled my flights but Easyjet/CarTrawler refuse to amend my car rental. I can cancel it but because it is a 7 seater I cannot rebook it because none are available.
I have phoned the agent (AVIS) and they say that because it is a 3rd party booking they cannot/will not help.
- Never book a car using Easyjet/CarTrawler
Search using their site but book directly with the agent. You may still have issues but at least there is only one level of mal-administration to deal with.