Nedbank debits car finance installment before scheduled date without any permission

Hi

I have a problem with Nedbank. My wife currently has a car financed by Nedbank. This month Nedbank decides to debit my wife's account today, the 24th,when the debit suppose to go off on the 27th.My wife does not have any money now because she gets paid on the 25th and Nedbank took the only money she has in her account.if Nedbank does not sort this problem out, I am going to sue Nedbank, as we have a legal and binding contract stating that the debit will go off on the 27th