iPod nano 6th gen invalid serial number

My 6th gen nano has a hardware issue. The volume up button is physically stuck in the down position, so I can turn the volume down, but never up again.

I am trying to get information on Apple servicing on their website, but whenever I put the serial number into the window, it tells me to use a valid serial number.

I took it to the Apple Store, and one of the staff told me that my nano was still under warranty for several more weeks. I went back a couple of