Fanatical and all of the discount sites are basically “you bought it, you own it, no refunds.” That’s part of why they offer discounts, it’s kind of a risk you take.
Issuing a chargeback for a product that was delivered could land you in court even if it works. More realistically will result in Fanatical permanently banning your account.
Never buy a game on these sites if you are at all uncertain about it. There is no refund and the key has been exposed.