Fill out a "False Change of Address" form on the United States Postal Inspection Service website (see Resources) and submit it electronically.
Contact your local postmaster to tell her of the fraudulent change of address and inform her that you have submitted a "False Change of Address" form.
Ask the postmaster if she has any information about the location where your mail may have been forwarded. If she is able to confirm that she does know this location, ask how you can change the fraudulent address back to the original mailing address.
Contact your local police department to find out if you can file a report, and do so if possible. This will likely depend on how much information you have regarding the details of the fraud.
Contact the three main credit reporting agencies: TransUnion, Experian and Equifax. Inform them that you have been the victim of a fraudulent change of address. Find out what you need to do for damage control purposes.