first of all don't know how long you been in the biz ,but i am wondering what your turn around on pay was. did your customer or the prime who handled your invoices not q.c. your work and let you know that you were billing wrong(chances are they changed your invoice and billed accordingly,MONEY IN THEIR POCKET).sorry for your loss,but they do have what is referred to as a mechanics lien... dont know what you are out($)but you are due what is owed to you..good luck and happy holidays..