Hi Simon and welcome to the forums.
Sorry to hear about the problems you have with TT.
From what you say you have tried all that you can possibly do from your end... aside from double checking roseways good advice and making sure that you have tested from the master socket.
There should hopefully be a test socket behind the master socket which you can also try.
Details
http://www.kitz.co.uk/adsl/troubleshooting.htmHowever, Yours is not the first case where TT have simply refused to believe that adsl is not working, despite evidence to the contrary.
My own brother moved over to TT in Oct and has had similar problems. Despite doing all the usual modems, master socket etc he just could not obtain sync with the exchange, previously he had a perfectly good connection with another adsl provider.
TT refused to believe there was no sync and Ive lost track of the no of new routers that they sent out... worse was he was even without even a landline for several weeks, as they also managed to take that out too. :/
The problem seems to be getting TT to believe there is no sync on the line.
>> Talktalk insist that the line has been setup correctly and there is an ADSL signal.
Challenge them how they have asserted there is an adsl signal - if they do their equivalent of the BT Woosh test, then they should be able to easily see that you havent been able to sync.
In view of the fact this has now been dragging on so long, your only alternative would be to insist that you arent getting the product that they were contracted to provide therefore you wish to terminate your contract and go with another provider.
They will try and bill you for an early termination fee.. but stand firm that you havent received any service and they havent fulfilled their side of the contract, therefore you are under no obligation to be bound by the T+C's
All of the instances Ive seen where this has occured has been where TT have moved users over to LLU, so you will have to do a full cease and reprovide to clear your line.
If you have problems getting them to clear the line then theres info at the bottom of this page how to do this.
ISP tag still on your line.
Hopefully you can now convince them that you have had enough and they may pull out their finger and actually do something before you have to resort to a full cease.
Good Luck.
>> with what appears to be a built-in microfilter!
Possibly the BT equivalent of one of these
http://www.clarity.it/telecoms/adsl_secondary.htmwhich the previous occupants may have paid BT to install.