Nedbank MFC unauthorized debit order date

Nedbank MFC debited my monthly vehicle finance payment on the 20 Jan instead of the normal date of 26 Jan 2025 .Upon quering this the call centre consultant tells me they were running a campaign for Jan and they changed my debit date to 20th without my consent What bull**** is this sending clients a sms to opt out if you do not want debit to go through on 20 Jan.what would have happened if I did not have enough funds in my account .Nedbank needs to rectify this bull because my salary date is 26