Step 1: Go to https://www.kinguin.net/ or https://www.cdkeys.com/ and pick out the game you would like to get. After you’ve picked it out, go ahead and buy it. Don’t worry, the money will be refunded to you.
Step 2: Login to your main account on steam/origin/epic games/gog and redeem the code. After you have redeemed the code, log out.
Step 3: After you have logged out of your main account, create a dummy account and try to activate the same code again. Take a screenshot of the “failed to activate” message.
Step 4: Open a support ticket on whatever website you purchased off of. Tell them that you tried to claim the code, but it had already been redeemed.
Step 5: From my personal experience all they ask for is your order number and proof that the redemption failed. That’s it. They will either offer a replacement code or a full refund.
ENJOY THE FREE GAMES!