Wrong Billing

I took a contract with Telkom in October 2013, this month is my last month regarding the 24 month contract and usually when you don't want to upgrade you have to cancel the contract to avoid it from Continuing . Yesterday a person from Telkom called me to confirm the cancellation and yes I did confirm that I am cancelling not continuing with the contract. They cancelled, when I went to the Brooklyn branch to check my bill, they billed me R652. For what I don't know???? THIS IS MY LAST MONTH AND THE BILL IS SUPPOSED TO BE R350 NOT MOREEE. Please fix this thing, how I wanted to decide to continue but can I after this experience?? I don't think so