12 months contract but im paying for 13 month..

i took up a contract with cell c and it was a 12 months contract in august 2014 which was my 1st month. at first they loaded me that im on a 24 months contract when i took up a 12 months contract. i had to fight with them to get it corrected. now that the contract has ended they tell me that i must cancel a contract to end it. why did i take up a 12 months contract when you guys debit me for 13 months. when u take up a contract with other companies u pay for 12 months and they cut the contract no need to cancel. i went to the retention to cancel and the agent i spoke to was rude and she didnt even let me speak or she couldnt even explain to me nicely on the procedures or why must i pay for the month that i dont want. i hate cell c and i will never recommend it to any one because since ive been with them its been nothing but fights. :(