Unauthorised debit

I have a made a restructuring on my loan after I made a lumpsum repayment. After paying a premium of R2843 after a few months they decide to debit R6700 which is my premium before it was restructured. My debit orders will bounce because of their incompetency and now I'm told to wait for the money to reflect before they can refund me. I want my money now, I cannot afford to have unpaid debits because of their incompetency