Unauthorized debit by FNB

FNB deducted my account without my consent today. They deducted the account monthly fee without my consent, the deduction was supposed to be deducted on the 24th as I know but when I checked my balance this morning I found that fnb have taken my money without my consent. My debts will bounce back tomorrow because of fnb since I budgeted for those debit as usual. I called the fnb General enquiry but only to be told that they don't know what happened, this conduct scares me because it means my money is not safe if they go into my account without consent any body can. The law states very clear that no one can go to a person account without their consen.