Cell C Doing anything and saying anything to sell

Hi I have been going back and forth with the Cell C agents and I and so tired right now . My basic story is that I upgraded my contract and was told that I will be able to switch up my contract at any point with no cost . Under 7 days of using the contract I knew I was not the right fit and I went to the Cell C service centre I was told but the Agent that its no problem but I will need to come back after 3 months because I did an early upgrade so I did so . I went back the Monday and now I am told I must come in on the 1st of the month because I can only upgrade then and that there might be a cost . I was really angry at the manner this was done and at the fact that I was miss sold this contract . Now I have excessive cell phone bills as an outcome . Could someone please assist me with this .