Debited despite the arrangement

I got debited R12k. I had an arrangement with capitec to debit the settlement amount of R2600-00 for a loan, instead capitec debited R12000-00. This is because the person I made arrangements with told me that it was not possible to arrange for a loan amount of around R8000-00 s it was already arreas, it was not going to be possible to pay it in parts, as a result, I requested that I first settle the small loan and then make arrangement for the remaining in January. I am not able to pay rent and other commitments because capitec decided to override our arrangement and instead debited about R12000.00. Please assist by reversingR10 000,00 and only settle the small loan. I will then arrange to pay the remaining over a period of 2 or 3 months.