Credit card charges

I have an Access Credit card with a credit of R15500 with Standard bank since October 2014 which is paid monthly via debit order. I used the whole amount once off and not again since. The payments of R465 remains fixed no matter the balance and I keep getting messages that my limit is over R15500. I have never had a debit order returned. I even tried depositing at the ATM, but the money is rejected with notice that my account has been suspended. I have visited the branch several times now and they phoned head office several times too. Last visit I was provided with ref nr *** from IT Group Services, saying they are working on the issue. I am really tired of struggling with this, as it gives me a bad credit record, showing the credit is overdrawn (and I am unable to correct it even if I try, since I can't make a deposit). I am very disappointed with the service,because I've been paying for almost a year without reusing any money and still my limit is 'overdrawn'. I would appreciate quick response from their head offices so this can be corrected.