FNB incurs unceccessary costs to its clients

My Mother owes money on a FNB Revolving Credit, she manually pays them every month, as she no longer uses the FNB Cheque account. She has called many times and asked that they don't debit the cheque account as there is no funds in there, yet they continue to do this, which runs up debt due to debit orders bouncing and she gets harrased with calls to please pay. She has asked they reverse the debts incurring and nothing happens. Surely the calls are recorder, and someone actually listens and surely the person that takes the call makes notes on the computer. When you ask to speak to a senior person, then suddenly there are no senior people that can fix this