Impossible to cancel contact

Tried to organize that my ADSL contact be canceled a month in advance of the date we would stop using the line, was not able to do this. Went into the Telkom Bayside branch the day my ISP released the line so that Telkom could cancel it but they say the line is still with my ISP, phoned my ISP while at the shop with Telkom employee but no progress made, emailed proof of line cancelation from my ISP to telkom employee and heard nothing. Went into shop with proof of line closure from my ISP, they still would not cancelthe line and instead gave me a case number. 1 week later and there has been no progress with the case number and I have just been send a new bill for next month.

I have done everything in my power to cancel this contract and they will not do it.