Cancellation of an upgrade

On the 4/08/2017 I upgrade with MTN Sumer Mobile. They said they deliver my phone in 5 to 10 working days. Iam waiting now almost 5months now for my phone and write plenty emails and phone calls that they must stop my upgrade. Very poor service from provider. They said my phone got lost between the warehouse and courier service. That is not my problem. I pay each month my account that I upgrade for BUT still no phone. Can someboddy please help me.