What do you do if you received a subpoena for a client you don't have. I tried contacting the agent on the document, but he never called me back.

First make sure that the subpoena doesn't cover times when I might have had the customer. Kind of obvious but...sometimes you gotta read those things over and over.

Then, write a letter stating the facts: you don't have a customer during the timelines that they are giving. If they have further information, blah blah blah, they can resubmit the subpoena.