What Should I do there’s an unknown Broadband ISP in my house?

You've just moved into your new flat or house and naturally you want to get your PC up and running with Broadband so you can keep in touch with the rest of the world. But when you try to sign up for Broadband, you find that the previous occupant had Broadband already and that your chosen ISP is unable to connect you until the previous occupant's ISP is disconnected and a ‘marker’ removed from the line. Worse, you have no idea who the previous occupant was let alone who that ISP might be. What do you do?
You might think that BT (who still at least provides the physical connection to your house) would be able to help. Not so. Along with the many advantages of deregulated telecoms comes this one. BT has no way to tell which ISP is connected to your phone. Instead you need to contact The Telecom Regulator OFCOM on 0207 9813040. They will give you a reference number for your enquiry, and should clear the existing supplier from the line within seven days. You should then check up with OFCOM everyday till the marker is removed, do not lose your reference number.