in many cases the person reporting you is allowed to remain anonymous, so, outside of consulting an attorney, unless you have proof who's doing it there's not much that can be done. just be damn sure that THEY don't have any proof they can back up THEIR claims with. lots of people are sitting in club fed for welfare fraud
File a lawsuit against that person. That would qualify for a libel case. Source:http://funadvice.com/r/1630q50018h
Wait it out. If you didn't do anything wrong, they won't have anything to prove the claim.
sue them for defamation of character..