No service delivery

I took out a personal loan from FNB and the terms of payment was a monthly repayment on the the 25th of each month instead FNB decided to deduct this amount weekly from my account and putting my account in arrears by charging me a fee of R115 for the transaction that could not go through due to insufficient funds. They charge me this amount 2 to 3 time per week because they keep on deducting the amount from my account. My cheque account reflects negative and also give me a negative freflection on my name on the credit berua due. I have tried to resolve this issue for the past 3 months by phoning and then use all my airtime without any assistance because they keep transferring my call to a different department. I even went to FNB kolonade branch where a consultant assisted me and promised me this issue will get resolved now because it is a system error which they have to fix and told me that they will reverse all the negative transaction on my account in order for my account not to be in arrears. It is still not fixed and I can not use my account because it shows a R2500 negative for all the R115' s which they deduct weekly for my transaction which they take **********ly.