Check you bank account when renting from Dollar Thrifty Car Rental

The sales office in Hatfield, Pretoria gave me excellent service, every time I visited the branch. However, when I have completed all business with them, I found that they have deducted money from my account without my permission. I was advised by the sales office that the claims office in Johannesburg has deducted the money, due to an accident claim. As far as I was aware all contracts have been closed with them. My bank account was dumped into a minus as a result of the deduction. I made them aware that this is causing serious problems for me with the bank. I was promised a refund, but nothing has been rectified. I called the claims office and was told that I must be patient and wait, even though it was not an authorised payment. I will now also have to carry the bank charges in order to remedy the account. I find this unacceptable that they can just have access to my account and take funds as they wish, and still have an attitude when mistakes needs to be corrected.