Extremely disappointed at customer service and service process at mtn

I took out a contract with mtn I have been a loyal customer for more then 6 years I have never missed a payment in my life . Today I had an issue where I wanted to block the phone that I am paying for every month I had to call you call center number 5 times every time I would call in they would want something that I could not confirm that caused me to keep calling them back . Eventually I went into a mtn store got a copy of my contract and when I confirmed everything to them they advised they cannot send me confirmation that the phone has been blocked not an SMS not a email nothing. When I asked what if the person who has the phone now calls in and ask them to unblock it will they just do it the consultant did not say a word.

The whole of point of me blocking the phone is cause the person using the phone did not pay me and is refusing to pay me and now my service provider can't assure me that they will block the the device as per my request