I usually tell them that the postal service shows it was delivered (date). Perhaps someone else in the household got the mail and didn't tell them? Then I describe my packaging. (Small brown bubble mailer, white bubble mailer, box, whatever).
Often a family member has gotten the item and the spouse doesn't know. Or that's what they say. That has actually happened to me as a recipient, so I know it really can happen...
See what they say after checking with family members.
You can also call the local PO and get more info if needed. Sometimes they can give more info.