What must l do to close this account

I have had a contract with cell c . After the 2 years contract they continued deducting when l called they said l was supposed to call them and camcel my cobtract . I mean my contract was for 2 years l thought it would automatically close after the contract is over last month they deducted twice from my account. I call ed and a guy said the amount reflects as a double l can reverse the one and still pay in R10 that is still hanging I reversed the other one and paid in the R10 now they say they cant give me a paid up letter as l have outstandin amounts and the second deduction does not show on their side . What do l have to do to close this account