I wish to cancel my contract

I'm extremely dissatisfied with the service I have received yesterday 23/02/2016 at Vodacom Clear Water. At about 15:30pm yesterday I called Vodacom Clear Water and spoke to some lady, unfortunately I never took down her name and I enquired about the upgrade of my line ***) and I told her that I'm due for an upgrade on the 08/03/2016 however I need to upgrade early because I don't have a phone anymore as my Samsung S4 mini is not covered for the damage of the screen (This was confirmed by Samsung). The lady advised that it's possible for me to do an early upgrade and that I just need to bring my ID and R150 for administration fees. I drove all the way from Johannesburg CBD to Clear Water to upgrade and get a phone. When I got there, some gentleman advised that I can't do an early upgrade and he can't assist me. I have my number with Vodacom for years now and I had other contracts with Vodacom previously but I have never been treated this way before by Vodacom. I also fail to understand why I can't pay whatever amount to get an upgrade done. Can someone tell me how much will it cost me to cancel this contract since I can't upgrade.