Unfair Acc debit

I have an arrangement with fnb debt collection,agency re an outstanding loan, missed two payments and advised debt collector that all outstanding missed payments will be made end sept, fnb debits my acc for 6mths instalments which I cannot afford, monies taken for school fees and rent, what am I suppose to do as I am trying,my best to settle the loan, requesting refund for 3 mths back as I am,nw financially stranded