Sorry i thought since you were responsible for the partner you had books and some knowledge
of the system .

so back to square 1
i would look thru the programming parameters of the fax and see if there are changes you could make and play with those changes 1 at a time

you did say its ext 27 plug in a single line
home phone and call x27 to see if it rings
also call the fax number and see if it rings.

also is there a voicemail on your system ?

also when you call the fax # does it just ring
with no answer?