How can i unlock my bt line when i change broadband providers?

I have cancelled my tiscali broadband and want to change to aol broadband. aol have told me that the line is block so they can not connect me. i have asked bt to unblock it but as of yet they have not done so they have told me i need a number to do this but i have no such number. tiscali told me that the line would be free after 7 working days however this was 3 weeks ago. what am i doing wrong or what can i do next.
Answer
Sounds to me tiscalli has left markers on the line, get in touch and ask them to remove them and you carry on getting same problem contact oftel