I would email firstname.lastname@example.org
They'll be the best people to help you with that problem. They usually respond pretty quick (they got to me in 24 hours), and seem very reasonable. At the very worst, you may have to "prove" you have the box. If you they ask, I'm sure taking a picture of the serial number would more than suffice.
Good luck. I'm sure you'll be enjoying Entrenchment soon.