UNFAIR BUSINESS PRACTICE

i have a contract with MTN, which i have not being paying since November 2018, the main issue for not paying the account, is that i previously had contracts with mtn for ipad air, Iphone 6 which both of them are out off contracts. I upgraded from Iphone 6 to Sumsung 8 around march 2018, unfortunately my wife was using the Samsung 8 and she was mucked in Pretoria. my concern is that my Iphone 6 was BLACKLISTED by MTN since October 2018 till to date. At the time i was staying in Mafikeng (north west province). I went to the MTN Branch at Bathopele mall in Mmabatho (mafikeng), i didn't get assistance since the consultant was clueless and she was unable to assist. i had to drive from Mafikeng to Pretoria Mainlyn Mall to query the phone around January-February month 2019. they look at the matter and called the head office to resolve the issue but they didn't successfully attend to the matter. My concern is that how can MTN Blacklist a Phone that is out of Contract. my name is Thabiso Matemane/ID No:***. My Iphone IMEI/**** ***. I can be contacted on ***