Complete lack of service to resolve an isduey

I closed my business down at the end of August. I have sent all the e mails, documents etc requested by Telkom to get the line disconnected. I have been into Telkom office at Fourways Crossing and not one person will help me. My bill was paid up to date and now I am receiving bills for that line. So someone is using the line. Where do I go to get decent service?