I have been trying to collect for 3 years now. I have sent certified letters called, faxed emailed etc. but to no avail. Every 6 months or so I get a fax requesting abstracts to be completed. Then I call and say I won't do anything unless you pay me what you owe me. They ALWAYS say 'we are cutting the check now" or "I've got the check right here"  I tell them when I have the check in my hand I will accept more work. They are so full of excuses, I even wrote the owners of the company who called me back very quickly and said she was cutting the check right now. That was 2 years ago. No check. Just be careful.