Refund for call of duty mobile purchase

• If the purchase is already made then I am afraid a refund is difficult. However you may try --> If you have an issue with an app on App Store or billing --> Request a refund for an App Store or iTunes Store
• If it is your device then, please --> Use Guided Access with iPhone, iPad, and iPod touch - Apple ... before handing over a device to a child.
• If it is your child's device then in future, enable ask to buy feature --> Request and make purchases with Ask to Buy - Apple Support

Unknown Charge

• Curious about a Charge? --> If you see an 'itunes.com/bill' or an unfamiliar charge on your statement
• If you have an issue with an app on App Store or billing --> Request a refund for an App Store or iTunes Store
• You can also request a refund for a recent renewal of an in-app subscription.purchase 

Phishing

• Beware of --> Phishing & Other Suspicious Emails 
• Know how to --> Identify legitimate emails from the App Store or iTunes Store 
• Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams —> Use these tips to avoid scams and learn what to do if you think your Apple ID has been compromised.