Telkom blacklists me due to their incompetence

Telkom has blacklisted me. Wow - what a disgrace. I recently tried to get a new phone contract only to discover that Telkom had blacklisted me for not fulfilling my payments. I was tired of their mediocre, trouble-ridden ADSL service so I went to cancel my account. That was the start of this nightmare. After multiple attempts and visits to Telkom branches, I was told that there were experiencing issues with cancelling the account (it was not a contract). That was in June. I advised them that I had a new internet service (from mweb) which was due to commence in July. I proceeded to disconnect from their services i.e. unplugged ADSL and phone. I started using MWEB in July. Telkom, however, continued to bill me for a service I wasn't using. When I saw the debit order come through, I went to the bank to reverse it. I couldn't pay for a service I was not using. It was not my fault that they couldn't do a simple thing like cancel my account - after giving them protracted notice. Telkom then changed the debit order details and they took money from my account again in September, and I went to the bank again to reverse the debit order. I have now discovered that they have blacklisted me. How can I be blacklisted for their incompetence? This is an egregious display of Telkom's modus operandi - a pain to live with and an even bigger pain when you attempt to sever ties. It is really pathetic that my credit record has been tarnished by their incompetence.