My honest advice ? Raise yet another broadband fault via your SP. Insist that the SP mentions possible REIN in the notes.
When the engineer arrives, he will
have to perform various tests, and they will undoubtedly
all pass. He is well within his rights to just close the job at this point.
If you explain your utter frustration with the problem, and relay your evidence to him regarding REIN and the effects on your neighbours etc etc, hopefully he will progress the fault onto the REIN team,
if the relevant criteria they need has been met.
As I continue to drill home, as OR engineers, we only have to ensure that 'our' MPF is fault free and capable of carrying DSL. We DO NOT (as yet) guarantee speeds, so unless you have a 'No synch' issue, or a 'Dropping connection' issue that is prevalent when we are on site, or a high-error count issue ..................... then I'm afraid it is down to how the engineer proceeds if everything is testing OK.
I truly hope you get resolution on this soon.