Loan being miscalculated

The bank made a mistake by not augmenting the debit order instalments on a personal loan, additional to this a cash payment was made, the bank admitted to the mistake being made and have tried to rectify this. The problem comes in by the so-called \outstanding\" amount being set into a \"new\" loan. We have tried to rectify this in-branch as we do not agree to the outcome of the first, yet the new account has been loaded and the instalments are being actively debited although affordability has not been confirmed. I wish for a senior accountant to look at the account and have proper re-course taken in terms affordability and outstanding amounts as the bank has to carry their fair share of the mistake."