Deducting payment earlier than due date

I just received an SMS from ABSA vehicle finance stating that they will be deducting my debit order tomorrow 28/11 due to it being Black Friday. My instalment is due on the 01/12. They deduct before every time for no good reason. I cannot wait to be finish with ABSA they are the WORST bank ever. If they deduct before it is due, am I going to pay LESS interest? I will reject the debit order and will fight you every step. It’s not legal.