Telkom - Overcharged due to late cancellation and now I have a negative payment profile. Thank you!!

Submitted cancellation documents via email well in advance . Emails were read. Kept following up. Account was closed five weeks after the cancellation date. I have been overcharged and refuse to pay and now have a negative payment profile. Have been trying since November 2017 to get the matter resolved without any success. I call and email every week, and absolutely nothing happens. Have referred matter to the Credit Ombudsmen, but still no resolution. I will NEVER take out another Telkom contract, no matter how good the deal. If the deal was free, it could not entice me to deal with them, EVER AGAIN. Their admin is absolutely useless and in my dealings with six or seven people, I have spoken to one, who I can commend. Have sent 19 emails and made countless calls, all to no avail. I have rated 1 star only because it is not possible to rate less than 1 star. In my opinion, they should get negative stars.