Cancellation request not acted on

I sold my house and sent in a cancellation request for the 16th Feb 2018. I sent this request in December 2017 to make sure that there were no additional charges and that Telkom received the request timeously. Telkom then cancelled on 1st January 2018 instead of 16 February 2018. I then had to phone and explain that the form is for the 16th February not 1st January. eventually they re instated the line but did not cancel it on the 16th February 2018. The new owners moved in and in April I was still receiving accounts for the line plus interest for non payment. after numerous phone calls and emails Telkom passed a credit, however, they did not credit for charges one month after 16th Feb and now owe my an additional credit of over R 500. I have been requesting this every month since then and now having received my October invoice I can see nothing has been done yet interest charges are still being levied on my account. I have lost patience with this and am looking at asking an attorney to deal with this