Multiple contacts of the same thing

In 2018 I took a contract with mtn(data - router) . Around September 2019 my son lost the sim card and I had to make a sim swap. They stupidly make a new contract. In 2020 around May I canceled my contract which was taken in 2018 without knowing I have the same data contract that was taken in 2019. After some months I got massages from company called VVM( credit collector)telling me that I owe mtn R1750. I went mtn shop at Rustenburg waterfall mall several times to clear this but they keep sending emails to head office which I never get feedback. I paid VVM the whole amount in January 2022. Now I am getting calls, massages and emails from another credit collector telling me that I owe mtn R5720. This the most horrible treatment a person can recieve. I wonder how many credit collectors I should pay to clear my name ftom mtn books. I get harassed by massages and email daily. I terribly regret the day I joined mtn.