over charge my credit card with about R14000 2rent

I have rented a van on the 14th October which R6000 was withdrawn from my credit card upfront and when I return the van R4213.33 was with drawn again and on the 23/10 I rented van again R2000 was withdrawn from my credit card upfront and when I return the van R1903 was withdrawn again, I ve been quering this transactions since the 28/10/2015 Avis said is the bank the bank said is Avis, The bank send proof of transactions which i forwarded to Avis but still with no luck, My credit record is affect as my credit card is overline due to Avis, Up today no one is able to assist me. I am very frustrated as the bank is calling me everyday to deposit money to credit card