Debit my acc, without my knowledge incorrect billi

I had a nice suprise on the 28 oct, when I discovered that MFC had debited my account with the amount of R840, without my knowledge or permission. Their reason is that they claim I am in arrears, but I am not, and they do not consult with me as the client. They simply just debit my account. Now tomorrow I have to pay another R2840.? Please this is ridiculous. I was dealing with a gentleman called Byron Davids who works in collections and he emailed me and we cleared up the matter, why is MFC systems not updated? and why must I as the client suffer.Please resolve.My emails and phone calls have gone unanswered.