What does it take to cancel a contract with Telkom???

I've done everything necessary, and been told on at least two occasions that my contract with Telkom has been cancelled.

I sent all the documents required 2 months before I moved, and have been in my new home for almost 6 months already. Telkom is still sending me monthly bills when I know for a fact that the ADSL line was cut off on time just before I left the old place.

I've now also received an SMS to pay R600 in the next 48 hours to "avoid additional legal collection costs". Why should I be paying for a service and competence that I never received?

The only thing I've done wrong in this process was ever agreeing to a contract with Telkom.