Hidden costs

I hired a car from Europcar for two weeks at a good daily rate but when I returned the car they charged me excessive daily rate for being a few hours after the hire time even though I put the time in on my booking, They did not alert me by email or tell me of this additional cost when I took the vehicle. I am not happy with the service and will not use them again. When I complained the lady said that I must read the agreement but this does not appear on my agreement.