welcome to the BT community forum where customers help customers and only BT employees are the forum mods
in order for the forum members to help please can you post the adsl stats from your router you may need to 'show detail' to get all stats (if hub enter 192.168.1.254 in your browser and navigate to adsl or if HH4/5 then go to troubleshooting then logs and you are looking for 2 line together when hub last connected to internet and they will show your connection speed and noise margin or if netgear enter 192.168.0.1). Then run btspeedtester (MAC users may have problems). when first test completes then run diagnostic test and post the results ( do not reset the router).
are you connected directly via a filter to the NTE5 master or test socket or to somewhere else? Is the master the only phone socket in your home?
Have you tried the quiet line test? - dial 17070 option 2 - should hear nothing - best done with a corded phone. if cordless phone you may hear a 'dull hum' which is normal
Someone may then be able to offer help/assistance/suggestions to your problem