Some good news at least, but only one number that I have found which exactly matches an 0845 number that belongs to Tiscali.  

The Smart Talk Retentions department, which is the department to contact to cancel your service uses the published number 0845 688 7574.  The real geogrphic number which seems to attach to this is

[glb]01787 884204[/glb]

The other numbers in this range do not match exactly to the 0845 or 0870 numbers.

I have put the Retentions number in the unverified list.  This office is in Sudbury, but if it's any help, the Customer Care and Billing line is in Chiswick.

Also,  0845 665 1665, listed against Smart Talk in the database no longer works.  Please could you change this to remove this number from that particular entry.  Thanks.