Telkom: Quick to sign up, impossible to cancel!!!

I tried to cancel my telkom account 10 months ago with a cancellation letter that they had sent me that filled in and I emailed it back to them and I spoke to them on the phone. Everything was supposedly sorted out. 6 months later I received an invoice stating that i owed them R3000 and something, which is strange since I cancelled my account. I went into telkom and got them to resend the letter again, they said it was sorted I just had to pay them R700.00 which was what I apparently owed them so I paid them the R700.00 hoping that this would all be cleared up now. Another month went by and I never received anything and the another month went by after and I received another letter stating that they were blacklisting me and handing me over to lawyers, so of course I went back to telkom to see what was happening, and they said they would sort it out and I resent them the letter for the cancellation with the proof of date etc, and they didn't sort it out. On the 13th of May they said it was sorted out, on their system it shows that I owe them money but after talking to the billing department AGAIN they told me i was actually in credit with them for R1360.00. I now need a letter urgently stating that it was their mistake and I am clear of the blacklisting, and they say I need to wait 10- 14 days which is actually unacceptable. I need that letter URGENTLY because of future financial commitments and it is now hindering my progress for my future!! And on top of this they actually owe me money. I feel like i'm fighting a losing battle and my credit score has been affected negatively because of people who haven't done their jobs!!