atari2600land

US Postal Service? If it's a USPS tracking, just give it a day. Sometimes they mark crap delivered when they mean 'arrived at your local distribution center'. 

Is it a legit eBay email sent ? Sometimes fake emails can appear looking real.

1- Check all appropriate places for it to be. I once got a 'delivered' notice with no package. Turns out they stuck it in the parcel locker on our mailbox, but didn't actually lock it. I'm lucky I found it before anyone else just took it.

2- Wait an extra day. Some delivery guys scan all their parcels as delivered before actually dropping them off, so it could just have been left on the truck as such. 

3- If the above doesn't help & the status doesn't change, go to the Post Office & ask about it. Sometimes they can check in with the guy on your route and figure things out. That one's a long shot, though.