MTN provides the worst customer care in South Africa

I just seem to be unable to cancel a so-called month to month data contract with MTN. Every month I get a new invoice for the current and next month. Every time I dispute this at their customer care department. I have given them notice of termination on 28 February 2024. I have already stopped using the data by then. The modem was sent back via courier to some warehouse in Gauteng in March as the franchise office refused to take it.. Every time I get a call from a different customer don't care agent, who listens to the story, and at times I get a SMS with some message of my request being dealt with. It seems that the customer care system is completely overwhelmed and unable to co-ordinate the queries. The service at the franchise branch at Diamond Pavillion is as terrible, as they do not even deal with those contracts.