Impossible line cancellation

I have been trying to cancel a Telkom line for over a month. There was a miscommunication between the Garden Route Mall store and Call Centre during our move in April 2017. Instead of just moving our line, a secondary line was opened. From May I've been billed for two lines, even though the line at our previous residence is no longer in use. I sent in a cancellation form for the old line on the 10th of July and again on the 31st of July, but the line has still not been cancelled.

According to Telkom our ADSL is still with our current service provider and the line cannot be cancelled until the line is converted to a normal PSTN. Howerer, according to my internet service provider, this was done on the 25th of May alraedy.

(I was also billed for the installation of the new line, which is supposed to be free. This service fee was R638.55. I have disputed this on the 10th of July, but have heard nothing back).

Up until now I've been wrongfully billed for over R1300.

How diffucult can it be for a major telecom company to cancel a telephone line and get their billing right?