Billed after cancellation

In the first week of December 2015 my wife & I went to the Telkom Mobile store at Cape Gate Mall. I cancelled a Mobile Internet contract with them that had already expired, by completing a Cancellation form. The guy that was assisting me wanted a copy of my ID & then said he has entered the cancellation request into Telkom's system & that it would take 21 working days to process. This then meant that by the end of December 2015 the contract would be cancelled & that after December I should not receive any more Bills for this. At the end of January 2016, R249 was deducted off my bank account & I just received the February 2016 invoice stating that another R249 will be deducted. Why am I still being billed for something I cancelled in December 2015. Does Telkom think people have spare money to give away for their incompetence for not processing my cancellation form. I emailed Telkom Mobile with this story & their response is to send me a NEW cancellation form that I must complete AGAIN, so that I must wait another 21 days for them not to process my request. They have not said anything re the R500 I have been billed for NO usage.