MTN upgraded a contract without my concern

I took a cellphone contract with MTN in 2022 which I was supposed to pay for 24 months and I did after I have paid my last payment in April MTN was supposed to end my contract but they did not instead they upgrade my contract and signed up for me data contact which is R80 p.m on my behalf without my concern then I called for cancelation but they could not assist me then I sent an email which they responded that I have to pay a certain amount plus cancelation fee which I did still they did not cancel it so last month they uploaded me with the data that I stated they should cancel it so I decided not to pay now they have suspended my mtn numbers, I went to the store and explained the story then the lady who was assisting me called them and said I should explain, OK I did and the lady told me xe can see on their system that I did call for cancelation of contact and also paid the cancelation fee but the retention did not process the cancelation and that I have to pay again so they can unblock my numbers she said she is referring me to someone and they also telling me that there's a 3rd party involved I'm my situation that they are not the ones who has upgraded my contract but it's some other company so I should call them and ask them to cancel so now I want to knw how did the company knew that I had a contract with MTN and how can they upgrade it without my concern and without me signing for the new contract that I agree. It just doesn't make sense.