Avis claiming damages not caused by me

I was phoned by the Branch in Plett 3 days after returning a vehicle undamaged that the vehicle is now damaged?? I returned the car on a Sunday and received a call on Tuesday. I refused to accept it and the lady advised that she would get back to me. AVIS then proceeded to deduct a damage amount from my credit card. Without contact, without proof, photos and after having the car in their possession for 3 days before finding damage. Various calls to your customer care centre and promises for feedback has not happened. I have now been holding for 15 minutes again.