Personal loan NOT in arrears, who authorized FNB to debit my account before my salary pay date & agreed debit order date?

I have a personal loan with FNB which i pay for via debit order monthly, in October they tried debiting my account two days before my usual pay date (i have had an account with FNB for more than 8 years and all debit orders are scheduled for the 1st of the month) which obviously did not go through - this payment however was then taken on the 2nd of November for the October payment due. Since then i have been receiving notifications that my account is in arrears, tried speaking to a consultant about this and even after 5 mins of explaining that i am NOT in arrears, FNB early debited my account without authorization, she asked me so what am i doing about my arrears amount?? Absolutely useless!! Even my payment for November month was only taken this morning of 3 December with another message that FNB is collecting arrears payments??