Bad service trying to cancel my contract

Mtn service is very bad.You go to the shop they tell you to call 135, you call 135 then they tell you to go to the shop. I lost my phone in December 2022 and I have been trying to get my device blacklisted, however I am being told that my devile IMEI does not match the device I have on the box I have. The crazy part is that MTN insure reflects the IMEI that is on my box. I am fed up now, I tried to to cancely contract and they still take me back and forth. How difficult is it to just allow me to cancel my contracts and live and peace knowing that my phone is lost and I will no be able to replace it?