I want to cancel that contract

My name is Mandla I have a problem with Vodacom, they hired a company called Afrizone, this company gets Vodacom customers , they ******* me into agreeing to a contract of which I was not aware of ,I'm paying Vodacom an amount of R_423 and get a airtime of R350 , now this company called me sometime in May , saying that Vodacom is changing their premiums from R350 to R375 in no additional cost it's for me and I agree meanwhile they are extending my contract with Vodacom not desclosing to that , I went to Vodacom shop to upgrade my phone and that's when I was told that I've extended my contract they can't upgrade my phone , and I tried to explain to them that the person who called never talked about such things but they refused to help me