Telkom is the worst provider I honestly want to protest against them

Telkom has to be the most ********** company when it comes to their after service treatment. I asked last year February to cancel my contract, filled in the paperwork in store and serve my month's notice and pay as it is post paid which I did with no issues come June I was still being billed, I must have call the call centre over 30times trying to get this resolved to no joy, I remember the one consultant in October said they could not find not even one reference or log about my whole issues to begin with, I had no option but to go through the NCC route which believe it or not got me response in less than 3hours after it was declared an official complaint, I was then told investigations were taking place and I would have the contract cancelled. Come December I received numerous smses that my issue was with the billing department. In January I then tried to apply for credit for something else which was then declined due to a default on my record, I immediately contacted Transunion they confirmed that I had been listed for a default to the amount of R3505.06 by Telkom which is incorrect. Telkom said there was an outstand of R286.00 which I paid and they would delist me which would take 5-9 working days. this was on the 9th of February to date the default still stands on my record. Please may someone give me legal advise as to how to sue or something because I cannot follow up a contract cancellation with no communication