If you are the person this happened to file a complaint with the United States Postal Service office of the Inspector General. As they used USPS this would actually be mail fraud something the law enforcement arm of the postal service has jurisdiction over.
This seems like it would be considered mail fraud, and as UPSP was used they have jurisdiction to investigate it. I'm not sure how serious they will take the case however.
You can file a complaint at https://postalinspectors.uspis.gov/contactUs/filecomplaint.a... or by calling 1-800-ASK-USPS