Bad service FNB/Discovery credit card

Hi, I have a discovery credit card which is overdue for a few months but I have been in contact with them explaining that I am having financial difficulties. I recently changed to FNB and arranged for them to deduct an amount R100 and that I would increase the amount monthly to which the consultant agreed to on the 25/06/18. On the 26/06/18 they went and deducted R749 which I didnt authorize and when I called them to reverse the payment the lady(Adele) said they would not even though she acknowledged that they agreed to the R100 payment arrangement the previous day. I then requested to speak her superior and she dropped the call in my ear. I am dissappointed at in the manner they handled the situation after they accepted my arrangement.