Sorry I’m late to the party here.
The verdict is, after fixing various minor faults, that the issue is REINS
Interesting, but earlier you said…
when the broadband drops, so does the dial tone
That doesn’t sound like REINS to me. You mentioned TalkTalk, so I assume you’re on LLU. Have the engineers tried replacing the tie pair? I had a similar issue, which dragged on for months and countless engineer callouts. Finally an SFI guy brushed past the frame where my tie pair was and “the errors shot up,” as he put it. A quick swap and… perfection.
3 km line on THTG: 19/1.2 Mb/s with Sky
Previously: BT ISDN, Nildram, Plusnet, 186k, EFH, Be*, Plusnet (again), Pulse8