Being sued after cancellation

I cancelled the phone contract with Glocell now Cell C on 13 June 2017 after it has expired. That I requested proof that the contract was cancelled and they send me from pillar to post. That since I signed cancellation while my payment was uptodate, Glocell Cell C is sending me statements claiming R2 020.69. I enquired several times where they get the money but no response received and they only tell me I will be blacklisted. I wants assistance to get cancellation confirmation proof . I D no ********** 578081. Contact no **********