Deducted money without prior notice or arrangement

FNB just deducted an amount from my account today without prior notice, arrangement or phone call. This is unacceptable!! since when did it become a right just to take someone else's money without their knowledge or written consent! FNB should be ashamed of this. I was transferred from person to person and division to division just to reach a mailbox telling me that their is no space for new messages, this clearly shows nothing is being done!