welcome to the forum
when you are at your pc please can you post the adsl stats from your router may need to 'show detail' to get all stats (if hub enter 192.168.1.254 in your browser and navigate to adsl or use a-z, if netgear enter 192.168.0.1) and run btspeedtester http://speedtester.bt.com and post the results.
are you connected directly to the NTE5 master or test socket or to somewhere else? Do you have any phone extension sockets in your home?
Have you tried the quiet line test? - dial 17070 option 2 - should hear nothing - best done with a corded phone
Someone may then be able to offer help/assistance/suggestions to your problem