Cancelled Contract but still being billed!!!!

I called in December as my contract came to an end, the person told me the last debit will go off end January 2016. Yet again Vodacom bills me end February 2016!!!!. I am so tired of going through this with this company, three years ago they owed me money but sent my account to a debt collector only to find out that someone there does not know the difference between debit and credit. Now again we are back with the same issues, hence my reason for cancellation and not renewing! PLEASE RECTIFY and REFUND!!!!