What amI to to?

For two months now unauthorised debit order has gone off my credit card account. The "merchant" denies, and sent me prove, that my account with them is closed. The "merchant" at no point in time had access to my credit card details. FNB keeps sending me back to the "merchant" and the "merchant" keeps sending me back to FNB. I have never authorised any debit order to anybody against my credit card account. I have today spent more than one and a half hours speaking to five different departments at FNB and all they do is defend the bank's innosence in the matter. The emphasis was clearly not in assisting the client but rather defending the bank's reputation. I find this extremely insufficient as far as customer service is concerned. My issue has still not being resolved and I do not know who to turn to next.