Cancelled Contract 2 months's ago and still being

I was due for an upgrade to my Cell C contract on 1st Feb 2016 and decided I would upgrade to the new Galaxy S7. I must have sent 5 online requests for a sales person to call me, and received no replies by mid Feb, so went to a Cell C store, only to find that there was no stock. I called Cell C sales and asked them to upgrade me, but by end Feb I still had no reply on my order that I had placed with sales, and in fact they could not find my order! The offer that I had wanted expired at end Feb, so being very disappointed with Cell C's ineptness, I called their Cancellations dept and cancelled my contract. They assured me that there would be no further deductions, yet I have been billed for 2 more months consecutively.