False Information Provided on recording!!

During the latter part of November 2017, when I called in to cancel my contract , I was offered to sign up for a package that included data and airtime only - using my current device. I had explicitly asked the agent if during this packages' time (24 months) I can upgrade to another deal (one with a device) I was told that "ofcourse I can do that- the company would get more money and hence they'll allow this" Now- when the time came for me to get a new device, I called in only to be told that I can only upgrade in August 2019!!! The agents promised to cal me back and I haven't received a call back after caliing in three times! I wish to cancel completely with Vodacom as I've lost all trust with their service and promises!