Debited My Account without Consent

Shocked yet again. Today is the 18th December. My debit orders are scheduled for the last day of every month. I booked my car in for a service which is to be done today which I just dropped the car off at Audi. I kept some money to cover for the service but low and behold FNB took that money out of my account without my consent. This is a f%^$%#@# shambles. How the F&^% must I know pay for the service. FNB you MO^%$#@!^