Bad customer service

I am not happy with the way telkom deals wit their clients, I got an email about 2 months back from apparently their lawyers saying they have blacklisted me and taken the matter further with regards to a telkom line I had opened in 2017,which I was billed for until 2019 even thought it was not working, it had no network coverage, I could not make or receive calls from that number but I kept on been billed even after I canceled it. I took the matter to my lawyers which requested a settlement letter from them, as per my customer rights I was not at fault and I should not have been billed, after I forwarded their lawyers the communication between my lawyers and telkom their lawyers refused to continue with the case as they saw that telkom was at fault.