My NID has a cut-out for each phone jack. They just snap/pivot, and
the circuit is disconnected. Disconnect all of them. Then, one at a
time, reconnect and test the outlet, and see which one(s) work. I
assume that when you used the test jack, that you removed the jumper
cord that connects your house circuits to the common point.
I had a similar problem, and found that the installer had provisions
for only 4 circuits, but had connected 5, putting two together, and
didn't do a good job of it. Took me about 1/2 hour to track the
problem down. I made careful note of which jack now connects to which
If you have the older junction block with the screw/bolt terminals,
disconnect each line, and proceed as above. I crimped lugs on to each
wire pair to make connections and disconnection easier in the future
(a house I owned before this one).
Hope that helps..