Billed after service was cancelled

I cancelled my telkom fixed line service on 17 November 2017. My telephone line went dead on 18 December 2017. Although I only had a phone line until 18 December I was charged rent for the whole of December which I paid. I now received an account for line rental January 2018 for a line I didn't had.

The e-mail address ********** doesn't exist anymore.

Can Telkom please correct this and send me a zero invoice.