They keep billing me and wont cancel my account.

Since early last month (02-02-2015), I asked the Vodacom agents to cancel my contract as I wont be able to pay anymore and my subscription had ended. I then went to the Vodacom Store here at Welkom centre in the Freestate to ask them again to cancel it as it still had not been cancelled, they refused to help me. I called Vodacom again today, on the numbers: 082111 as I saw that they had AGAIN topped up my phone with airtime and I still was not assisted until they hang up. I simply cant afford to pay R365 every month as I'm no longer working and they seem to be forcing me to do that. Now im stuck with airtime that I don't want and no one is helping me with that. Please assist me.