So you have a problem of a broadband tag is still on your BT line even though you have no active broadband.
If you cannot contact the ISP for the Tag or they no longer exist, then the quickest method to remove as follows:-
1. Call 0800 800152
2. Enter your Telephone number when asked
3. Give Name , address and LN account number from your BT Bill when asked
4. Ask for a STOP/START on the line (this is 2 orders) and should be Free of Charge
5. Ask what is the consequence of this on your contract as it may restart the contract, in my case it renewed it for 3 months but it can be a year
6. Ask for a new contract that suits you not them. If they refuse to do it then tell them you will take your business elsewhere, as you have cable television, so could use cable telephone with no monthly rental fee