Account closed but still getting billed

I requested my land line to be cancelled on 31 October. I sent the request a full month earlier, as is required. Telkom did not attend to the request, and only sent an SMS in December stating they regret losing me as a customer. However, I am STILL getting billed on the line, and currently "owe" R657+-. I ahev not sued the line since end August (as proven by Telkom's own records - NO calls made). Fortunately I am not on a debit order. I refuse to pay this account, since I gave the 1 month notice as required by my Telkom contract. Can someone competent please close the account and reverse the charges?