I need help!!! Im being robbed!!!

I worked a Vitas case through my agency. It was a home case . they normally have carbon copies of charting for agency nurses to take home to fax to prove they were there. Well this case had no carbon copies for this home case. I signed in and out for the night.Charted Q 2 hours. 2 weeks later I still have not been paid because Vitas mysteriously cant prove I was there. I am mad , angry and down right PO'ed beause my agency is now saying that they cant pay me unless Vitas approves...if they dont....that means I pretty much worked for free that night....( 13 hour shift by the way)

WHAT CAN i DO? I am tempted to get a lawyer involved, I am just so mad!!!