In message <37arm31nr7vd2h7i82ftmah643vvib0nsl@4ax.com>, brightside S9
<address@replyto_is_not.invalid> writes
this for you.

I had an almost identical incident recently with the same router. After
a mains power spike the router seemed to get itself into a tangle and
the ADSL connection was continuously dropping and reconnecting every
minute for a couple of hours. A router reboot fixed the problem at my
end, but by then the exchange had decided the line was noisy and
increased the noise figure - and of course dropped the speed.

I was told that 10 disconnects in an hour will trigger the exchange to
increase the noise margin - it will apparently adapt back down itself,
but needs a period of several WEEKS stable connection to so do.

Apparently BT are reluctant to do this manually unless there is an
incident, that does not seem likely to reoccur, to explain the
disconnects.

After raising a ticket with them, my ISP (Plusnet) contacted BT and had
the limit reduced to 6dB and everything went back to normal. The process
from fault ticket to increased speed took less than 24 hours.

Contact your ISP again and lean on them. Blame the router!!

--
Peter R Cook