Non refund of a deposit and extra charges

We booked a car at the Cape town international weekend for three days 27-29 November 2015. Keys were handed over together with the rental agreement which noted no damage to car. we inspected the car with one of their staff members are damages were found and were noted down on the agreement. We returned the car on Sunday as per the agreement and later that day I got a car from Avis informing me about the damage. I explained to the person that there damage was there when we took the car and even sent him proof. But to our surprise money an amount of R6417.26 was debited and repairs and admin. And when I call am taken from pillar to post. All that I want is Avis to take their rental money of R2800, petrol of R104.00 and their contract fee of R64.00 and return my R3 446.26. Failing which I will escalate the matter to consumer commission.