[Enjeve]

"Please remember that you are legally binding with your signature that you only received the package with one article."

You're claiming that you didn't receive the package, so this doesn't relate to your claim.

Ask them to elaborate on what they're referring to.

He also left a note in the mailbox, where the package can be found.

The above clearly demonstrates that the package was left unattended at your premises. This solidifies your SE, regardless of whether they try and state otherwise.

Take a copy, email It, and ask them to explain the driver's actions- namely why he decided to dump the package and leave thereafter.

Thanks for the quick reply! So I don't have to fill out the PDF at all?
Also, I forgot to mention that on the card the driver left here, it says: "A package in the cabinet in the carport" and the date of the delivery.

Does the statement "in the cabinet" make things more complicated? Since yes, "actually" no package thief is making the effort to look into the cabinets.