Cell C *****ing money for canceled clients

I have now tried for almost 4 months to cancel my contract with Cell C, I have called several times, I have emailed several times and I have even spoken to a manager which assured me that the matter will be investigated however after 1 week since I spoke to a manager I still have no feedback. How hard can it be to cancel and stop a account, it's terrible that I get billed even when I called to cancel 4 months ago...the worst part is I was told upon inception of the contract that it will be a month to month contract yet I get billed every month even when it's been made more than clear that I have canceled. Cell C is the worst fiber internet provider, slow internet, poor customer service and appalling billing team...HOW MUCH MORE MUST I DO TO CANCEL WITH CELL C.