****med out of my deposit!

I'm extremely frustrated with Thrifty. I hired a car from them that had a couple of big chips on the windscreen. The chips were marked when I took out the car. I pointed that out to the guy who gave me the car and he showed me that its marked. One of the chips obviously developed into a crack as the car was being used. I clearly indicated that when I returned the car. I was not involved in an accident, nothing happened to me while I was driving the car. Their car was already damaged when I took it. The guy who received the car agreed that it was already damaged and he is going to tell his manager.

When I returned the car, I asked for my deposit for 2 weeks and they kept on promising that I will receive it. I call again today and I am told that the car was damaged, I wont be getting my deposit and I owe them. How when the car was already damaged when I took it?