if manually holding the recessed button on back for 20/30 seconds until lights flash does not solve the issue then phone customers services and get a replacement free assuming you are still in BT fixed term contract
you didn't say you already had new hubs and ended up with same problem
have you tried using the test socket with a filter and see if that helps at same time as using test socket check that you do not have a dial tone at any extension socket whether in use or not
as hh6 have you turned off smart setup? have you split the 2.4/5ghz networks to see if that helps and manually selected the wireless channels rather than auto?