Unauthorised debits off my card!!

On the 28 March, my business card was manually debited by Avis four times in a row for the amount of R1389.52 per transaction, totalling R5558,08. There is no reference or booking number. I tried to contact Avis via telephone and email to report it, with no success. It was only when I posted a comment on Facebook, that their customer service contacted me in the beginning of April. I sent them everything they required to show them these suspicious transactions, and have since heard absolutely nothing. They have however, managed to send many customer service survey requests asking about service (which I have given a low rating), and even that has not prompted a response. They are so quick to debit your cards, but do not resolve any queries!!! Can someone in Avis deal with my issue!!