Telkom do not cancel my account

I had Telkom ADSL at home and on April I moved to a new home so I asked to cancel my account. I filled the form, sent by mail as per the attendant request but I had no feedback. Next month I received the normal invoice as nothing had been done so I called again and for my surprise my account was active as nothing had been requested. Since them each and every month I've been trying to cancel my account but nothing happens. Truly don't know what to do anymore. On may I had to pay the due amount because I had to do a contract with another company and my name was in the black list. I hope that people can read it and be aware that is easy top sign Telkom but impossible to cancel later on.