I would strongly recommend you contact BT Openreach as they should fix what they broke! :mad:
If you don't want to do that, in theory all you need to to is re-connect the disconnected cable. As there is now broadband on the line and a filter face plate now in place of the old NTE5, you're going to have to re-connect the disconnected cable but after the filter face plate and to do that you're going to need one of these:
Simply plug it back in on the phone side of the filter face plate. The issue here is that should anyone unplug it, line 2 on the PBX will no longer work. I have attached another wiring diagram for your reference:
The question is this... Have you located the cable that BT disconnected or are you running a whole new cable to the PBX? If your using the old cable that BT disconnected how many cores does it have and what colors are they? Popping a 430a plug on the end of the cable closest to the BT socket wired as shown in the first diagram above should be all that needs to be done! ;-)
If however you're running a new cable from the BT socket to the Panasonic PBX then wire it as above at the BT socket and connect the White and Red to the outer pins 1 & 4 of the RJ11 connector (see 2.2.8 Types of Connectors in the installation manual).
The installation manual can be found here bt the way: http://www.overline.com/assets/Overline ... manual.pdf
I should point out that the manual doesn't say if polarity matters, I myself would wire th RJ11 as follows: white to pin 1 and Red to pin 4. You could use a volt meter on the RJ11 that feeds line 1 in order to discover what polarity is being used on that line.
Good Luck :P