It would be better to purchase games like Sims 4 via Origin yourself. Or buy game codes via places like Amazon.com or other trusted online retailers. Or local retailers. - The game code may come in a box, or on a card. - The game codes are one-time use only.
That takes the hassle out of trying to get EA customer service to help with the game code, as they may or may not be able to help with getting a new code. - They (EA CS) may tell you to just purchase new anyway.
Origin is legit. It's EA's game client. - However, selling an Origin account with the game included is illegal and should be reported.
You must use Origin to Play Sims 4. You can log into Origin using a different account than the one you have purchased Sims 4 with. However, that account will not have access to your Sims 4 game or other Origin games you purchased with your other account.
Origin isn't set up to share games in-between accounts.
See the link below for more information on where to buy EA Games, such as Sims 4.
Where to buy EA games
https://help.ea.com/en/help/faq/where-to-buy-ea-games-v2/Be aware that both Amazon and Walmart have marketplace sellers. These are 3rd party sellers that can sometimes sell the same items, such as games. However, they may not be on EA's trusted online retailer or authorized sellers list.
EA/Origin may block game codes that come from 3rd party sellers or unauthorized sellers.
If you purchase games through any unauthorized sellers, you will need to work with them to get a refund for the game, as EA can not help with this.