Ripped off for the warranty case

We rented a Ford S-max minivan to go skiing to Austria. The car was all the time located in the secure car parking in front of the hotel. Unfortunately, either due to the cold or snow, the car window cracked. There was no sign of any external damage. When I returned the car, a member of staff told me that it should be no problem. When I got home, I saw a bill for 500 euro. I feel that I got ripped off for nothing(manufacturing defect). Good luck in resolving this issue as well, the expected response times are longer than 7 days.