Dunno about this, but its best to cut out the serial numbers from pics instead of striking them.
People are able to figure out somehow - saw some post in reddit - some guy wanted to give out keys but it got stolen.
I dunno, better to wait for others to respond who might know better.
But since it does not say that the code has already been used, maybe try to contact both seller and amazon support.
I saw one review on the seller who seemed to have had the same issue and seller did not respond.
Also, amazon page says 'EGames Kart (Authorized Distributor of Steam Keys)' which may be false ( dunno for sure ), so this is on amazon too.
Hopefully, this is a mistake by the seller and they will fix it. Maybe code is not activated ?
Op, I'm sorry that you are out 5k it seems, but honestly, how do you order from someone who has to write in their store name that they're the authorized distributor?
If I start introducing myself as the pope to everyone I still dont think i'll be able to get a ride in the popemobile.