One year later and still struggling with these people

Last year in July, I gave notice to Cell C to end ****le stick contract. They read the e-mail, but did not cancel the contract. End of that month, I received an invoice. Again I contacted them, they said they will cancel, but did not. After that, books of communication has been going on between me and Cell C, but they do not credit the "arrear" amount as they are suppose to. They handed me over to attorneys, and I explained to them as well the whole useless situation. Yet, they keep calling me. And now my credit score is affected as I am APPARENTLY 2 months in arrears with Cell C (WHICH I AM NOT!!!)