Billing me for two contracts

Last year i have upgraded my telkom contract (***) to the new iPhone 6 plus which was about R500 per month which i signed for. Then i get billed R1500, and there after R950 each month, i have never used the sim i just upgraded for the phone. They told me i get billed for two contracts a iphone 6 plus and a normal iphone 6 and i need to go into the branch to get this sorted, i cant see why i need to go in and sort this as this is a problem on telkoms side.