bad service by telkom

we have cancelled the adsl and telkom line before 4 months and they are still billing, when call them first they always they off line and if we lucky to get response they will transfer one to another, send them many mail but they dont response. as we had 3 business line and want to cancel one, we are in business for 12 yrs and cant effort loose main line, that is the reason we have to continue with telkom as we have no choice. very bad service