Vodacom the worst company to do business with

I have been trying to cancel my data contract since 16 October 2020 when it was a month notice to cancel it. I was told it was cancelled then I got a bill in Dec and have since then called every month and keep getting told they will review the calls and sort it out. I have now been listed as a bad payer as I have an outstanding bill with them which I refuse to pay and nobody is prepared to sort this out. They say they have the logged calls and will escalate it but nothing gets done. I am now at my wits end with them