I've been experiencing loss of Broadband a few times over the past few months.
This last week was bad, sometimes it was there ok, sometimes it wasn't
After spending quite a while with (Indian) CS, and confirming everything was OK in my house, finally got 2nd Line Tech number (UK).
They eventually sorted the problem.
Even though on my router Internet & ADSL lights were ok, indicating sync, no Broadband connection.
Turns out it was the Line Noise setting, set by TT tech. (whatever that is)
The operational band is 6db to 15db, it had been lowered to 6db last year, and was trouble free for a few months.
Doing tests today, the techie and I agreed on a Line Noise setting of 12db.
So, if you're on TalkTalk (or any other ISP provider) and have problems with Broadband, try different Line Noise settings, as set up by tech chaps.