MTN not removing the blacklist on my phone

I am very disappointed with MTN's service lately. On the 8th of August 2018 I lost my phone and i then phoned MTN to block my sim card. The person I spoke to at MTN advised me that they do not block sim cards but they blacklist the phone and in order to that they need the phone IMEI number. I gave them the IMEI number and the phone was blacklisted. I asked the lady what will happen in the event that my phone is located at a later stage and she indicated that I should just phone and the blacklist will be removed. I located my phone and phoned MTN as instructed. The person I spoke to this time around said i need to sent through the affidavit and proof of purchase in order for them to action my request. The documents were sent on the 13th of August 2018. The service from MTN thereafter deteriorated badly because I didn't hear from them for more than 48 hours and when i phoned i was given another email address to sent the documents to which I sent. After a week they asked for the same documents which I sent. Now MTN is gone AWOL on me and I am sitting here with my phone which i cannot use and MTN is not bothered and yet its supposed to provide service to us. Why have mechanisms to block something if its going to be difficult to unblock it when requested by clients. I am very disappointed.