I also made the mistake of accepting assignments from DFS last year.   I was successful in forcing payment from them when I reminded them that their terms stated that any legal action must be filed in their jurisdiction.  This meant that when I was successful in my suit against them they would be required to pay my filing fees and other costs to collect (travel in order to appear in court) in addition to the monies owed for the three closings I had performed.

This will only work if you have documentation of the terms of the agreement.  The first confirmation they sent me did not show my fee, it listed $75 as their normal fee.  I insisted that my fee, which was well above $75, be listed on my confirmation and would not call the borrower to confirm the appointment until I had been provided with a corrected confirmation.

Good luck.