FNB Credit Card Not Following The Agreed Arrangement

Its been more than 2 years I left FNB & went to another bank due to their misleading customers & making customers life miserable, I joined FNB credit card with a limit of R5000, I made an arrangement with them to take money every month from account to pay off the funds that I used, all of a sudden after I think 6 months, the bank calls me & told me that I have overused my card & skipped the limit now I owe R9000 I asked them how is this possible but I got no proper answer, I left them & joined another bank, since then till today the Credit Card Collection Dept for FNB has made my life very miserable, every month I call them to make an arrangement, we will agree with the arrangement but they never stick to the agreed arrangement, each month they go straight to my account & deduct huge amounts of money (R7000/ sometimes R6000 & this month November 2018 =R5393), I am willing to pay my debt, I make arrangement with them but each month they just do totally the opposite of what we agreed upon, in the begginning of this, I called again the Collections Dept for my credit card, I explained to them my situation of each month, the lady advised me to pay R2000 & make Special Arrangement with them, I paid R2000.00 I called the collections dept, we made the Special Arrangement of myself paying R500 each month until the debt is completed, few days after that I went to the branch in Bloemfontein, we called the collection dept, they confirmed the arrangement with me, of myself starting this month to pay R500 each, SURPRISINGLY, again this month the amount of R5393 from my account, my question is what about our "Special Arrangement " as they call it? Someone please help me, every month I have to go to my bank to reverse the debit order of FNB not following their agreed arrangement? Is this fair to me? More than 2 years the same thing has been happening, I get extra bank charges from my bank because of this, my bank statement always reflects Unpaid debit orders. I want to pay my debt of the credit card, but I cannot afford to pay the full amount, I followed their advice of paying R2000 so I can follow the arrangement of R500 each month but its not happening. Please intervene. Regards M. Kori