Super irritated with TELKOM

I'm super irritated with Telkom, because I closed my contract with them beginning of 2019. Telkom owe me money and today, I'm shocked to learn that Telkom put my name on the black list. How can they do that when they owe me money? It is so unfair. I have all the correspondence between me, the people of Telkom: Nomathemba Mokoena and Shaun Smith their collection Agency Management. I'm trying to call Shaun, but with no success, please Telkom take my name of the list!