We understand the frustration when USPS indicates they have delivered a package and you can't find it. As a reminder, once a package is picked up by USPS and leaves our facility, it is no longer in our control.
USPS is responsible for packages in their possession. Contact your local Post office to find out where your package was left.
Occasionally, packages are left on the property behind bushes, in a courtyard, by the garage or left at a different address. It happens.
As a seller, we advise our customers to contact their local Post office branch, the location from which the package is dispatched for local delivery. USPS scans the package when delivered and they can tell you where your package was (mis)delivered and where it might be retrieved. This is something only you can do since we have no insight into the delivery beyond the tracking number once it leaves our warehouse.
Here is a link to an article "USPS says Delivered but no Package" that can provide some means for getting help from USPS.
In these unfortunate instances, please contact your local post office to find out where they delivered your package.