Cancellation of Contract

My contract with cell c ended in March 2019, and as per their rule i phone in January and in February to cancel my contract as i do not need upgrade, to my surprise this contract is not yet cancelled . i am aware that i owe them outstanding amount that was in arrears but i am not prepared to pay another month that they were supposed to cancel. it is really frustrating to deal with Cell C customer care, today when i called to query the R838 that they say i owe them was told that contract is still active.