Telkom Account handed over to Debt Collectors

In short, I had an internet line installed by Telkom which I cancelled in Nov 2018. I paid the account and was under the impression this account was paid up. The line number was ***. I received no correspondence (invoice or final account) from them up to today. They handed me over to debt collectors without my knowledge. I paid the debt collectors today 12 July 2019 with their costs included off course! If I was aware of any outstanding amount I would have paid it in time. This affects my credit rating because of incompetence from Telkom side. I am furious with their service! I demand an apology from them and my credit record to be cleared.