WAS THIS A REVENGE MOVE FOR CANCELLING WITH CELL C

I CALLED IN TO CANCEL MY CONTRACT WITH CELL C AS THE CONTRACT WAS FINALLY FINISHED. They told me that there would be 1 more payment coming off and I would be finished with the contract. So yes the last payment went off and lo and behold they decided to debit my account on the 25th of the month. My debit order was always for the last day of the month, now suddenly they take off the last payment on the 25th. I am only paid by the 28th of the month thus making my payment bounce and a MESSAGE FROM MY BANK (ABSA) WARNING OF A DISHONORED PAYMENT. My account now look's bad with my bank and I had to pay the charges. What on earth are these people doing to suddenly change a debit order date with your bank and you aren't even aware of it ???