MTN TRYING TO **** ME

I took a contract with MTN I think in 2016 or 17 which I immediately cancelled the following day after discovering the best option with another network. I was asked to pay the cancellation fee and a ref number was issued. I made that payment and use the ref no.. All of a sudden I am being harassed and Im told that I need to pay my debt and this is the company that handling my case- Account Name: NuDebt Trust Account Bank: ABSA Branch code: 632005 Account Number: ***. Reference number: ND***7. I told the agent that I spoke with yesterday that they must take this matter to court because I am not prepared to make another payment for a service that I did not use. I feel like MTN is trying to **** me.