MTN upgrade department

I did an upgrade a month ago and it was approved but up to now there is no delivery of the device,I have tried to phone the courier company and they claim that they tried to deliver the device on the 8th of feb but they never phoned and when i ask them when they will deliver it they dont know.I have tried several times to phone mtn and each time they tell me that Elstern will phone(whoever this elstern guy ) but still nothing has happened.Now im tryng to cancel the upgrade because mtn failed to deliver the device to me.Can someone assist me with the cancellation of this contract please.