Cancelled contract but still gets billed

I have been trying to cancel my contract with Vodacom since April 2017. On 25/04/2017 I phoned the call centre to cancel my contract and was informed that it had been done. I followed up on 02 May 2017 after receiving another bill and I was informed that there was a final amount to be paid before contract can be cancelled - which I paid immediately. To my surprise in June I got yet another bill and phoned again, this time they stated that the account was supposed to be closed but the cancellation was just not processed as yet. This became the trend month after month, I receive a bill, I call in and they tell me a lot of stories. They eventually started to credit my account for the months incorrectly billed, but the following month yet again I was billed. In October 2017 it came to a point where neither the customer care or account or retentions could assist me due to the account being suspended due to non payment and nobody apparently has access to do anything on the account unless I pay the arrears amount - which I refuse to do. We are now at a point where I have been handed over for non payment and still after numerous calls to Vodacom nobody could sort this out. I have been billed for December 2017 and January 2018 yet again. I have spoken to every possible person in rank over the phone, even went into a Vodacom store but they couldn't assist. I do not know what else to do, this is ridiculous.