How do I cancel my phone line??

For the last week, I have spent hours on the phone trying to get hold of the call center, I have sent an email with a reference number I got from a response on Twitter, and I have tried calling the call center again, to no avail! Either the line gets cut off, or they tell me that my line is being hosted at my ISP. According to my ISP the line HAS BEEN CANCELLED on their side, they even refunded me the last payment FOR THAT LINE! The number in question is ***, and my account number is ***. I will not be paying for ANY services after this month, as I cannot get hold of anybody to CANCEL such services. Please use this as my official request to have that line, DSL, telephone, EVERYTHING associated with that account number, cancelled.