Account Cancelled. Second bill after cancellation

On the 2nd of December 2015 I submitted cancellation for my Telkom services after receiving a mail with a form. (I cancelled a month earlier and it was never processed). I was phoned back and notified that the service will be cancelled as of 24 December 2015 as it was supposed to be cancelled on 24 November 2015, and that I would not be billed. They took a debit order at the end of December 2015 and I have just received an account for end of January 2016. This is utter nonsense!!!! I want my money they took at the end of December 2015 back and this account stopped immediately or I will be proceeding with legal action against Telkom. This is nonsense and utter pathetic service!!!