No refund on my authourity funds and its the 2nd t

I rented a car with Avis and they took they authorisation fee so I extended 3 times and they kept on taking the authorisation's fees which added to R6300 so I returned the car n they debited my account with R8000 for the rental days ever since I've been checking my balance calling the call centre nobody is assisting. The only thing they do is to send me up and down getting statements from the bank.