None response from Vodacom legal team

I sent several emails on the 5th and 19th December 2022; 12th January and 21st March 2023 to request that the legal collection investigate whether I was not double charged for the non payment of my son's cellphone account that was registered under my name while he was still a student. I settled the outstanding amount and a year later I received another notification threatening on the same issue and I asked my son to contact them and make arrangements. He did so and settled the account. A few months later I received another notification threatening on the same issue that I would be blacklisted and my account will be closed if I don't pay by a certain date. I contacted the Collectors and explained that I had settled previously and they told me that Vodacom sent them that I was still owing and so I need to pay or else face the blacklisting and closure of my cellphone account. I believed at that time that Vodacom used different Debt Collectors for the same account. I settled again and decided to write to Vodacom legal requesting that they should investigate the possibility of me being double/triple charged but haven't received anything from them.