The Clearcom system generates a call by putting a DCs voltage on the Audio on pin 3
Check between pins 1 and 3 and see if you get a DC voltage when the callbutton is pressed.
Its not clear from your post but aside from the Call not working do you get any audio?
Personally I would try connecting each of the beltpacks direct in to the MS-232 one at a time with a known good cable and see if you get Audio and Call signal both directions. This will help rule out a faulty pack and the Main station.
Next step would be to check your cables for breaks and shorts.
Did you change, add, remove anything to the system at the time it stopped working?