Lol. I keep getting receipts showing my letters were delivered. How do the replies keep getting lost in the mail?

Green slip sounds like the return receipt part of "certified mail, return receipt requested.". Really, the post office should be returning those, since it's a service they pay for.

That is, if they're even paying for real certified mail, and not trying to forge their own green slips.

This isn't working! I better spend a few more thousands of dollars to figure out why!