FNB: wrong deduction dates.

I took up a loan with FNB and the date we agreed on for the 1st deduction was 25/10/2018. I then logged online and saw they had changed the date to the 5/10/2018. I called to get this corrected. The system changed it to the 25/09/2018, the person assisting me (her name is available if needed) told me that it has automatically changed itself to September. I then told her that I signed on the dotted line cause the date in october was the date that suited me and my financial situation, no That September. She now tells me that I must call and ask that it be reversed or reverse it myself after it has deducted!!!! Like WHY!!! Over an error on FNB’s side! WHY when I will incur costs for doing that. This is no error done by me, it’s an error done by fNB! Fix this mess FNB! That’s how you can help me.