cant get celllphone blacklisted

I Mr Apollis NO#*** have been a contract customer for more than 15 years with MTN. I am dissatisfied with the service i am receiving with the MTN call center. I have been trying to blacklist my ****** phone from the 10th of march. on the 25th of march i was on the phone with them for more than 30 minutes speaking to a George, on the 26th of march i was again on the phone for 30 minutes plus. Today i have tried again with no success. calling to the call center has been a utter waste of my time. because of this my insurance has now refused to pay because my phone has not been blacklisted. I don't even have the option to cancel my contract because its only six months into the two years and the cost makes it near impossible. So now i sit with no phone because of pathetic customer service.