Misinformed when signing a contract

I kept my subscription to Smart M when I upgraded the end of June 2015. The post is very unreliable and I've been wondering why my phone bill has been so high, thinking that it must be the extra calls I made. To my shock I saw that I get charged an extra R290 a month for the iPhone 6 that I upgraded to. I would never have upgraded to that phone if I knew I had to pay R290 for the handset a month! I obviously cannot remember who I signed the contract with but I should certainly have been informed!!!! I hope there is something you can do to help me out of this predicament. I know I signed the contract but shouldn't the salesperson make you aware of the extra charges that you will incur??