I'm pretty sure they have invisibility potions or the power to cloud men's minds. Twice they managed to attach a "sorry we missed you" slip to my screen door while I sat 10 feet away with the door open.
Similar experience with DHL.
The building of my apartment is shared with a convenience store owned by the landlord's son. I picked up a package there, and they told me that the DHL guy had, two days in a row, been here knocking loudly on my door to deliver the package to me.
Like you, I was about 10-15 feet from the door, @ my computer. No headphones, no loud music. I'd be able to hear a
cat pawing at the door, and certainly a rather dull delivery driver pounding on it repeatedly.
No idea what the deal was there, but in any case, I got the package.