Telkom price increase

Hi, there's something about telkom, they have this specialty of crawling in ur skin just to make sure you can never win with them, I signed a 2 year contract for my ph line and adsl which was on a special, now couple months down the line they have a price increase and this was never mentioned at the time of signing that we'll be affected, they so sweet to promise you the world and made me understand that it's a contract and the price stays the same for the full duration of the contract, called the billing department they say sales must assist me in this regard, called the sales department they say existing contract should be honoured at agreed prices and only billing department can do the adjustments, called the billing department they blankly refused to even look into the matter to charge me agreed upon price per month, now I'm stuck with a 2 year contract at a higher price, who can I speak to to resolve this matter for me