First National Bank
Denied changing an incorrect debit order date

I have a personal loan with FNB which mistakenly had the automatic debit order date set to the 23rd of each month. Not something I would have set up because pay day is the 25th of each month.
For the past 4 months I have called FNB every month to switch this date to any date after the 25th and have done so unsuccessfully.
The response from them, "It can't be done, but don't worry, the debit order will not go off if you don't have the money in your account".
FNB, you can help me by fixing this very fair simple request, or I will be moving my business to a bank who will be happy to help.