FNB transfer money without my knowledge or authorization.

FNB once again transferred money from my cheque account without informing me, or with authorization. I logged a query with them, no response. I called the call centre, no joy whatsoever, being transferred to different departments the whole time and no one knows what to do really. I spend over an hour on my cell phone and no joy... So they take my money without my knowledge, and I have to pay a huge cell phone bill and still the matter is not resolved. I demand FNB to pay me back immediately, this is the worst customer service from FNB, and I will be forced to take my banking to another institution.