Be careful of unauthorised charges - I have been ignored for years

I have been an MTN customer since before it was called MTN (Z-Tel then) and I was posted abroad temporarily in 2007, so I maintained my SA 083 number on a reduced contract. All went well (I was a very happy MTN customer) until around 2019/2020 when a new and UNAUTHORISED charge of over R200 a month appeared on my monthly bill. From London, where I was based, I queried this unauthorised charge, and the charges for some three months were reversed. This speaks volumes about the charges not being for my account, I think! Then they restarted and MTN refused to identify who the Contents provider and show me proof that I had authorised this charge. Indeed, the Customer Services people said I should dial a number (local and not possible from UK) to cancel it and would help no further. I repeatedly demanded proof that I contracted for this service (all emails saved and filed) and I even pointed out that my phone was not a Smart device and could not be used for anything but calls and SMSs. Phone calls (at my cost as I was abroad), letters to Customer Services and the MTN Legal Dept (two named individuals with one Bowden) were unsuccessful in having this travesty of customer service and customer protection rectified. I even wrote to several Board members with copies of the emails I have filed. Is this a company people want to deal with? MTN allowed an unauthorised service provider to bill me and collected on that person/company’s behalf. After being a happy customer since virtually Day 1, I expected something quite different. Does anybody else have this problem? How can we allow such bullying and unconcerned service continue?