It is indeed the 0.9mm Cu feeding your premises, well remembered.
My sole aim here, is trying to understand
why the refusal to fault one of your lines has been agreed ??
There has to be validity to it, as I suppose you could flag this up to Ofcom and they (knowing this) would have to provide some kind of supporting evidence as to why services have been withdrawn ??
They can't simply turn round and say 'He's a nuisance'

Just to cover old ground again here, probably 5'ish years ago, a 'High Repeat Report' team were established to cover exactly your kind of issues.
Having been involved with broadband from the very start, I can tell you that in the first few years the training was woeful and the engineering support was too. I myself hold this very forum on a pedestal, as a massive aid to my own personal development in this arena.
So, please believe me when I say that the 'HRR' team that was set-up, was manned by very knowledgeable individuals who could scrutinise circuits along with the best. Coupled with access to other systems mentioned earlier in this thread ... they were found to be a fantastic asset as the time consuming hard-work had all been done, by the time the engineer had picked the fault up.
What I'm trying to imply I suppose is my guess is that somebody of that ilk has done a whole lot of cross-referencing of previous fault reports, outcomes of said reports, general stability of the circuit, performance in relation to other nearby circuits etc etc ...... and decided to draw a line under it.
Not for one minute am I suggesting you don't have an actual fault condition on L$ (or whichever one it is ??), I'm trying (and maybe failing) to get the message over to any of the readership viewing this, that over-scrutiny and constant fault reporting can have an adverse effect
if the
perceived issue falls within the ISP agreed 'Cone of Acceptance'.
I reiterate, there has to be a valid reason as to why they have stopped raising fault tickets.