Telkom - most useless company?

I duly gave notice for my ADSL Landline last year in May, received confirmations of this notice for the various TIN numbers, moved out of the property ... and to this day I receive an invoice every month! It has now an astronomical amount of +- 12 000 Rand. The first three months or so, I still phoned the accounts department, explained the situation over and over (what is there to explain, actually?), spent literally 100s of Rands on airtime trying to sort something out that should have just been smooth running. Lawyers letters arrived, which I answered as well, as they are threatening to affect my credit rating!! I am at a point now where I simply ignore any correspondence but yet, it bugs me that this company seems to consist of useless, ineffective, unprofessional and unwilling employees.