In addition to the above advice about copper/ADSL, if any of your sockets are still live after unplugging whatever you can and/or you actually want to use a phone, you should also plug filters into ALL of your live sockets (whether they have something plugged into them or not).

For the ultimate, cleanest & best connection you can remove the faceplate of the master socket to reveal the "test socket" [1] (which in so doing disconnects every other socket in the house) and then plug a filter & your ADSL modem directly into that socket, or fit a replacement faceplate e.g. [2],[3]

[1] http://www.hmmm.ip3.co.uk/bt-master-socket-nte5.shtml [2] https://www.amazon.co.uk/N247-ADSL-FacePlate-Filter/dp/B0030... [3] https://www.run-it-direct.co.uk/adsl-vdsl-faceplates/vte2015...