Resistance to cancel UNAUTHORIZED / *****ULANT upgrade

I received a call on 04 Sept from Summermobile regarding a upgrade. The call got disconnected before anything was confirmed or accepted. The next morning got a sms from MTN regarding the successful upgrade that was done. Ever since that Tuesday 05 Sept, i am struggling with MTN to cancel or reverse the upgrade, to enable me to go and do a proper upgrade and get a handset. The handset that they upgraded me to, is now missing and thus i am paying for a "36" month contract with nothing to show.