I have had the very same experience with them.  they owe me
$320.00 from January and February of 2004.  I also called and
faxed, but to no avail.. They had several offices earlier, as I was
doing work for one in Indiana. They closed, and I was told to
deal with their Florida office also.  I finally gave up, which is
probably just what they want.  I also do not understand people
who keep doing work for companies who do not pay them. 
I have had this happen several times, and have posted about them
too, hoping to inform others to be wary before going in the hole
too much with any one company.  I've never thought about going
to the underwriter.