MTN bad Service

I canceled my contract with MTN in 2019. I had to pay a cancelation fee for the contract to be canceled and my number was removed on contract to prepaid. However I have been receiving calls and messages from a certain company stating that I have been blacklisted due do my failure to settle my MTN bill. This confuses me because I paid the cancelation fee and now I'm blacklisted. I have been calling MTN and they keep taking me back and forth with no solution to my problem.