Problem with Summer mobile - never asked for a upgrade

I am having problems with Summer Mobile who is contracted with MTN. I have been upgraded without my consent. i have been contacting Summer mobile to cancel this upgrade and have no result. I do not upgrade with a third patry except directly with MTN. I need your support with cancelling this upgrade and dealing with Summer mobile I have now received SMS with a phone which i have no idea. How can i take a contract without knowing what instrument i am going to receive, Don't i have a choice. From the 9th I am contacting Summer mobile to cancel this contract