How do I get a refund from Apple for double-charged Monopoly GO purchase?

Apple Account purchases are always processed as an Apple Charge on your billing statement. I suspect the Amazon charge is for something else . You can view what your Apple Account purchases are for by going here:

View your purchase history for the App Store and other Apple media services - Apple Support

Amazon provides this documentation for viewing their charges labelled as Amazon Digital. The App Downloads noted as possible charges is not the Apple Apps for your iPhone, they are for apps specific to the Amazon devices.

https://www.amazon.com/gp/help/customer/display.html?nodeId=GSNBBJP63SM65UDB

This is a user to user support site. The people responding on this support forum are users like you. We have no special access to Apple information or your accounts, so unfortunately all we can do is guide you to the information Apple does provide. Apple, however, does not have much on its criteria for refusing refunds. Below are two sections from the U.S.A. version of Apple Media Services Terms and Conditions - Legal - Apple Media Services - Apple You can see if the terms are different for where you live by clicking on this link Legal - Apple Media Services - Apple then select your location and then your language.

- "All Transactions are final."

Apple's terms of purchase in the USA are, "All Transactions are final," ( Legal - Apple Media Services - Apple section B), but check the terms for your country. Even if Apple does not outright say in a country that sales are final, they may say that refunds are only made to remedy defective or unavailable product. In other cases Apple may make limited refunds solely at their discretion and as an exception. Apple can also simply say no without having to provide a reason. I understand this can be frustrating but by using the service you agree to the terms.

- "From time to time, Apple may suspend or cancel payment or refuse a refund request if we find evidence of fraud, abuse, or unlawful or other manipulative behavior that entitles Apple to a corresponding counterclaim." Remember that Apple has no way of removing a purchase from your device. They have to trust you are being honest when asking for a refund. It may be that certain refund requests might be considered suspicious or excessive.

According to https://reportaproblem.apple.com/static/en-us/privacy.html , Apple uses an automated system to detect fraud. Your request may not have met the automated system’s criteria for a refund. In the article Apple says, “If you disagree with your final decision, contact dpo@apple.com “ However, according to user posts on this web site the result is confusing because you receive an automated response talking about privacy issues, not refunds. In that case:

If you wish to try a telephone or chat method, click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.

or:

"See a list of Apple phone numbers around the world." Click here --> Contact Apple Support - Apple Support