Matt,
   I had a similar issue with not being paid for a search I performed. After several attempts to contact the company, I contacted my E&O carrier and explained that I wanted to send a letter to the company to tell them that if they continued to ignore my request for payment, they should not expect to benefit from the protection of my insurance. I was politely told that if a claim was ever made, regardless of whether or not my invoice was paid, they would pay a valid claim. Fortunately, I was able to resolve my issue.
         I would suggest that if you have E&O insurance, check with your carrier.
Christy