I've got BT (business) line and NTL (private line + TV) for over 15 years.
I used to have internet as well with NTL until they started messing up.
I decided to part with them about 18 months ago.

After disablement I was forced to close my business.  
I could not afford to keep two lines on my benefits so I decided in April to end my telephone line with NTL.
They accepted  to cancel from May.
Then I got a call to say that they will refund me my next 3 months line rental if I just continued with them.
Then I got the bill and surprise surprise they 'forgot' to refund the line rental and charged me even more for my TV package (even more than the new increase).
I phoned on the 0800 number and was reassured that they will only charge me £3.50 from the next month and other charges will be refunded.

Now this will make you laugh: The next bill for June has arrived and surprise surprise they have had another memory lapse.
They 'forgot' to credit my refund.
Then to add insult to injury, the new 0845 phone kicked in.
So they deliberately make a mistake so that earn more money from unsuspecting customers who complain.

I rang their 0800 number but was met with announcement to ring 0845 number.
I rang that number and spoke to an agent.
She told me that the previous agent had not put the details on their system.  
I told them to credit my account with the line rental and the cost of my 0845 call to them.

Needless to say I have given them one months notice to remove my phone line.