Your best bet is to first check with any roommates, neighbors, building managers, leasing office, mail room, and any other people in the vicinity to see if they may have picked up the package.
Also give it 24-48 hours, sometimes mistakes happen and packages accidentally get marked as “Delivered” up to 48 hours before the actual delivery even though they are waiting at the post office.
If your package is still nowhere to be found please email help@susansown.com for next steps. Please include your order number and your full name.