Unauthorized Payment

I'm generally a huge supporter of FNB as a bank and have been a happy client for many years now. That was until today, I'm sad to say FNB authotized a payment off my Cheque Account without my knowledge for a large sum, when contacting them to try resolve how they could do this they moved me to 4 different consultants each telling me that the payment was for a petrol card. The more I tried to explain that I don't have a petrol card nor did I I authorize any payments the more they kept insisting that I do. When asked if they could reverse the funds I was moved to the next consultant to explain once again what had taken place. The next consultant hasn't bothered to respond to my enquiry and has left me waiting. Not the service I have come to expect from FNB, and no the resolution I was hoping for. Very disappointed and out of pocket.