@KurisuK36 Okay two sides to this, (one side is to explain EA support's response).
1) If the code was bought but not received, (as in you're still waiting for the code from Amazon), then yes, EA support can't help you with it. You'll have to contact Amazon about it since the purchase wasn't through the game, and thus can't be looked into by EA support.
2) If the code was bought, received, then redeemed, but the coins weren't added to your account, then EA support should be able to help you with it.
I think the reason why they had "blamed Amazon", was because the agent had thought you were still waiting on the code. Try telling EA support that the coins weren't received yet and have them look into the code not working. Even though the codes are from EA/Respawn, the codes are randomly generated, so EA support can't do much about the code itself. However, I'm hoping EA support can see that you had redeemed a code recently and that the coins weren't added.