credit card billing

I have manual pay my Credit card on the 16 July 2015 .<br> on the 17th Fnb credit debited my account(debit account) with the same payment R1500 this amount was returned unpaid in my debit account and cost me R100 and on the 20 July again fnb debited my account with R2000 which again costed me R100 as it returned unpaid from my debit account and right now am receiving smses asking me to make a deposit of R1986 in my account and i have called the fnb line so many times and sent several email with my statement asking for explaination for this July month debiting .<br> <br> I was promised a call back but i still yet to receive it and i have asked for the debit order to be cancelled so i can make the payment on my own to avoid such situation and i was told it not possible .<br> <br> How many R100 must i pay daily due to this debit being sent to my debit account.<br> <br> Please correct the error and reverse the unpaid fee charged in my account as my july payment was made.<br> <br> I have lot of reference numbers for every call i made and email and am not receiving joy .can someone please explain the whole thing <br> <br>