One more test you can make and that is for a high resistance fault. Bring up the router stats pane and make a phone call, ringing your own number would do. Keep an eye on the noise margin when you are doing this and if the noise margin jumps up, that conforms an HR fault. There is nothing you can do about this personally, but if you pass it on to the BTO engineer when he comes, it will give him a clue what is wrong. If the noise margin does not rise, it is some other type of fault.