No updates on contract

I have a contract with Mtn and somehow I fell back on my payments. And it ended up going to Mtn legal. So I paid the full amount I was owing. And I wanted to do the sim swap. And I went to Mtn store many times wanting to sort this as I was told that my number is on the old system they don't have it on their new system. And as much as I hate my name being on the blacklist it's like they are enjoying it as I don't have info on what is going on with my contract. I'm hurt