Duplicated Key

Sadly no

if the key is already use then the game is possibly useless due to needing the code.
not sure if there is another way to play without steam if steam is required
i have the same thing with Half life 2 so ended up paying for it from steam store

Return the game, they MUST give you back your money.
If it requires steam and they sold it as second hand, it must be illegal to sell it.

99% chance you cant as its already redeemed but when you have spent you can try one thing as the previous owner fooled you by selling such game. You can write to steam support that you bought the game but the key is not working. Mention the case number (with pencil) on the serial number and upload it as proof of purchase. Steam will unbind the game from the previous owner and give you the key. Chances are around 90% you will get the game.

I would insist on getting my money back. They probably don't know that theses games need to be activated at an online platform and can't be reused once somebody used the key.
Get in contact with them.

You could take picture of the box and retail cd-key and make a ticket at steam support. Ive heard it's possible that they remove it from the previously owner.

You got scammed...

... mostly from the game companies releasing games on media but tying the license on the supplied (one use) key than the actual disc that was the norm before steam (and still is on consoles). Everyone has the right to resell games. Learn this well and don't buy any boxed stuff dating from the scam age. Understand what DRM is about.

Said so, i just bought older parts of the Heroes of Might&Magic games series - in boxed form. Which do contain a fully working self-contained games.

Telling so gamestop has adapted to this. They mostly (still) sell console games now. Other used game sellers have went bankrupt. Ideas were to introduce a similiar disk-less concepts on consoles too... Microsoft advanced first (Sony held back) and got their deserved shit-storm. But they will try to introduce such a system again later on - probably with the next console gen.

Who would buy a game that has obviously been used and expect it to work? There's a reason why new games are sold daily. Companies wouldn't make any money if everyone passed around the same disc and used the same key on their computers. Take the loss. It's your fault for trying to get something for nothing. Was the price difference over buying a legitimate new copy worth this grief?