Feeling Cheated

On the 25th April at about 4 pm my wife and I tried buying our monthly groceries and to our shock the transaction wouldn't go through due to insufficient funds. I went to the atm and realised that almost R4000 had gone missing from my account I phoned them thinking maybe another transaction had subtracted twice but the help I received was minimal. The earliest I could get to the bank was the 28th of April, at the bank I spoke to the consultant and was told I need to phone a number upon phoning the number I was told to phone yet another number. So I phone this number and it turns out that the debit came from MFC for a car I had returned to them two years earlier. I asked the lady how this was legal as on numerous occasions I had explicitly stated that I would not authorise any debit orders from them. I had however made arrangements to pay R200 a month into their account but my family have been having some financial struggle the last few months so I couldn't make the payment. She continued arguing that, that was the reason the debit order was made. My point being if I cannot afford R200 who gives them the right to take R4000 which is meant to feed my wife and 3 children. As far as I know a debit order can only been done if the account holder has given clear verbal or written authorisation. I'm honestly ready after years being a Nedbank customer to close my account and change banks. B Theron ***