Device is missing or not delivered

I have contacted MTN and summer mobile on numerous times trying to find my new cell phone. No one can tell me were the my package is or who is responsible for my package. Summer mobile did my upgrade and can not help as MTN should give the package to the courier services. I have called summer mobile and MTN and have decided not to pay MTN till i recive my new cell phone. Now i have tried canceling the upgrade that was done by summer mobile and they are not helping me to do so!! A lot of emails have been sent but still no luck! I am fedup and need help!