No response for cancellation

Ive been trying to cancel my telkom line from September. No response as yet. Still getting billed for this ****. Telkom doesn't give a **** about you and if you dont pay they blacklist you . So whats my options here?? The are quick to sign up new clients but when its the other way around never responds. I have contacted them a few times and the lady say to send the cancellation document again. Ive sent it now 5 times. Telkoms management is **** so use your cellphone and fiber or wireless and it will make your life so much hassle free.