Vehicle Finance Error

Nedbank has deducted a vehicle installment in error. On contacting them telephonically and by email, I was told that they had already processed the debit order beforehand and that they could not stop mine from being deducted. My question to them is, who is paying for my overdraft charges for their incompetence. They shrug their shoulders in apology for the inconvenience but are not taking responsibility & accountability for their error. Had the reverse happened, where I was tardy in depositing to my vehicle finance, Nedbank would have slapped on late payment charges PLUS interest on late payment. Why does Nedbank get away with this ? I was not able to cancel the debit order, either, as the banks have some insane agreement on debit orders..... I'm very annoyed at Nedbank.