Telkom incompetence and harrasment

I have and still have multiple high value contracts with Telkom (Mostly uncapped everything). I have always been on debit order. I have Telkom's third party debt collection company calling me for over a year now saying that there is R100 outstanding and I need to pay or I will be blacklisted. They say I need to prove that I paid an amount that was never outstanding! I have called Telkom at least 6 or 7 times over the past year and a bit, to clear this up. They keep promising that they will sort it out with their debt collection company, but still the calls and threats come. I have threatened to cancel all my accounts with Telkom, but still they haven't prioritized resolving the problem. My advice is, don't go with Telkom, they have the worst reception / coverage of all providers, they have a government institution attitude to customer service (non-existent) and they have three different business units, which can't communicate between them, I.e. (Mobile, business and home line service businesses) . If you don't heed my warning, you only have yourself to blame!