Early debit order payment

How does one change the date for the debit order of an FNB personal loan? Consultant asked which date must debit order go off and was pertinently told the 1st of every month but FNB decided not to honour that and made it the 25th of every month even though salary only gets paid 27/28th.. Phoning the personal loan account department proved fruitless as they said, (after waiting almost 9 minutes on the phone) that I should phone end of next month again?? Messages on Facebook messenger also go unanswered but yet they will expect me to pay for bounced debit orders?? FNB is becoming more and more useless!!