contractual agreement

i have a contract with cell c. for a modem. i called in and asked that i don't want to continue as my contract term is over. i was advised that i need to give them a month notice and also they told me they cant as they didnt receive payment. i made payment arrangements and even honored the arrangement. and my port was closed. however they still deducted even increased there premium. every time i call they tell me about a month notice.its been over a year i have not been using my modem however i have not been using it. <br> <br> I have called several times with no luck.