Over a year to cancel Telkom adsl account and still no luck

Telkom service is appalling!!! I have sent them about 6 different emails with cancellation forms and even had 1 phone call back from them apologising that it is taking so long to cancel my contact, but after a year still nothing. Now they have handed me over to someone to collect the money, I have mailed them all the proof that I have cancelled my contact long ago and that they just kept on billing me. Now they have given me a bad credit rating by other service providers so I can't get new services. I have never in my life seen such bad service.