Amazon stole my inventory and sold it back to me!!! How can they get away with this!!

Amazon said they lost one of my items in a shipment...ok, I'm used to that...we all are. But then Amazon had 1 for sale which they hadn't previously. It's an odd title..so it struck me. I ordered it from my buyer account...and sure enough...it was my copy with my fnsku labeled on the back. They gave me a small reimbursement for the lost item...then turned around and sold it for $80!! To me!!! I will return it to get my money back...but that is absurd!!! Amazon has gone so corrupt!!! How is this ok??? How many of us are they doing this to???