They keep billing me and wont cancel my account.

I had a contract with Vodacom and my subscription recently came to an end as I was due for an upgrade and advised them I wont be upgrading. I called their agents on the 2nd of February this year and advised them to cancel it, they said they have done so. I later found out they haven't and made my way to the Vodacom store in Welkom centre and found out it wasn't cancelled. I then asked the consultant there to cancel it for me and she refused. I then called Vodacom after finding out they topped my account with airtime after i asked them not to and asked an agent to cancel it for me of which he kept me on hold and then dropped the phone in my ear. I am now unemployed and forced to pay money that I cant afford and stuck with airtime I don't want and no one is willing to help me. This is not the first time I encounter problems with Vodacom, they have the WORST service as they billed me 3 TIMES in the past! i would never recommend anyone to use it! Please assist.