Debit Order date of personal loan

I have a personal loan with FNB and previously also have other loans with FNB. I have had no problem with the other loans until the current one.

When i app**** i asked that the debit date be the 25th of a month (salary date). I called in and was told that my debit order was changed by the system which is messing with debit orders and my account. How can the system just change my debit order. I gave permission to use the 25th.

I then called the call centre and the lady was rude and not willing to help at all.

My company does not provide letters on salary dates as in some months (like December and February) this can differ.

I am now in arrears and need to change the debit order date back to the 25th. THE DATE I ORIGINALLY ASKED FOR. THE SYSTEM IS NOT ME AND I WILL NOT LET FNB PICK AND CHOOSE MY DO DATE.