Unauthorised debiting of accout

Fnb debited our account ********** 6436 with R731.83 x 2 on 30 Oct 2017. After taking it up with the branch, one amount of R731.83 was credited back to the account. We are still fighting to get the other R731.83 back. According to the branch this was a set off for a credit card debt dating back to 2009. If this is the case, then this debt is prescribed, as we have had no correspondence regarding this debt. Secondly if this is a set off, then this is done incorrectly, as the cheque account was in debit at the time of debiting it. You cannot apply set off from an account that is in debit. As a result of this we are currently sitting without funds for our monthly expenses. Your branch says we need to speak to Brooks & Luyt, whilst they say thqat they did not debit or instruct FNB to transfer the funds out of our cheque account. Please ensure that these funds are put back into the cheque account immediately, failing which we will be taking this up with the banking ombudsman.