The only thing I can think is
Posted by Joe on 4/19/2017, 10:10 pm, in reply to "Anyone had trouble with USPS deliveries?"
sometimes they won't leave it if you're not there (that's up the the mail carrier, unless you live in a an apartment with a mail room or front desk where they would always just give it to the staff) and sometimes the information doesn't update on time, so a failed delivery + failure to update properly could account for that. Even if you were home all day maybe you were wearing headphones or in the bathroom or something and didn't hear them knock? They should have left a note on your door or in your mailbox. If you have an outside door it could have blown away, but then we're piling up misfortunes to the point where it's becoming more improbable.
If you think you need to call them try doing it at an odd time of day rather than noon or after 5pm and my might be more likely to get through.