Unable to Blacklist my phone and swim swap

My phone is lost and I'm using mtn, I called the call centre to blacklist the phone and I was told that my number is a contract which surprises me because I don't have any contract with mtn. No one could help me from the call center instead I was told to go to the nearest mtn store, I went to 2 mtn stores still nothing. If I can't be assisted in the call centre and the mtn store then who must help Mr? On top of that I'm unable to make swim swap. Can you please help I need to report my phone within 24 hours to my insurance and the unfortunate part mtn is delaying me and won't replace my phone. I'm drained and angry.