I sent a CRRR to a CA's PO box and strangely enough I got a reply from them about a week later however I never received the green card....
I think that the post office puts the CRRR letters in the po box, assuming that the receiver will be honest, and sign the green card, tear it off, and drop it in the mail. But as you have experienced, they have kept the letter, as well as the green card. The post office would never know...
Years ago I used to work for a lawfirm and we got CRR mail all the time and we used a PO Box. The mailman would leave a notice for us to collect the mail at the counter. They never left it in the box. IF the Post Office is leaving the whole thing in someone's box, that seems to be a problem they'd have legally IF it could ever be proved. Mommy2cats
I DO IT ALL THE TIME WITH CREDIT CARDS I CLOSE... CA'S are different...the PO BOX is the "TRASH CAN"...
If you don't get the GREEN CARD in 10-14 days...the POST OFFICE can do a "DUPLICATE SERVICE" for FREE...
or you can log onto the site for the post office(USPS) and enter your certified reciept number and the system will verify the day& time it was delivered and signed for........ Ignorance is Bliss Knowledge is King!!!