Avis damaged vehicle

During December my insurance hired me avis vehicle which I got it on 18th December, so it happened that the car aircorn failed and I decided to changed it. Which I did it in East London airport. The vehicle i got at East London and the one that I was changing no one was willing to do inspections on the, infect they told me the person who's doing inspections is off. I filled and signed exchange form and they just gave the the key for the ather car. I returned the car to welkom which they checked the car and now they said I damaged the car and roughly paid it. Which I don't know about it and I never damaged the vehicle.