自分のゲームで他人がゲーム内購入を行った

As this is more of a security issue rather than a game issue, we recommend you contact the support service of your platform's store (Google Play or AppStore) to request a refund on unauthorized purchases.

How to prevent such issues from happening again

To prevent this situation from happening in the future, we recommend you to enable some safety measures on your device.

On Android

• Open the Google Play app;
• At the top right, tap the profile icon;
• Tap Settings -> Authentication -> Require authentication for purchases;
• Choose a setting;
• Follow the on-screen instructions. 

For more information about this functionality, please, refer to https://support.google.com/googleplay/answer/1626831?hl=en

On iOS

To lock down iTunes & App Store purchases or downloads:

• Go to Settings and tap Screen Time.
• Tap Content & Privacy Restrictions. If asked, enter your passcode.
• Tap iTunes & App Store Purchases.
• Choose a setting and set to Don't Allow.

For more information about parental control, please, refer to - https://support.apple.com/en-us/HT201304.