Debit order after cancelling

I cancelled my telephone line and ADSL on the 23/25 October. I was on a month to month contract and I understood that I still had to pay for November. But now Telkom sends me an invoice to pay at the end of December. Not going to happen. Someone from the accounts department better contact me as soon as possible. I will be stopping that debit order as I have cancelled and will not pay that as I have cancelled and Telkom can check their records as well.