protip: interference with delivery of united states mail is a federal crime.

You just talk to the Postal Inspection Service.[1]

Destruction, Obstruction and Delay of Mail (18 USC 1700, 1701, 1702 & 1703)
The Postal Inspection Service upholds federal statutes aimed at securing customers' mail, including those related to the desertion, obstruction, delay or destruction of mail. Postal Inspectors demonstrate their resolve by implementing mail security processes to ensure that customers receive their mail intact and free from outside interference.

...

Theft of Mail (18 USC 1708 & 1709)
Postal Inspectors invest significant resources into the investigation of mail theft by criminals.

EDIT: holy crap, I didn't realize that what this super did with OP's mail is punishable by 5 years imprisonment!