If you have done an accidental purchase of the app, you may claim a refund through iTunes. 

Click here to know more  Report a problem.

This helps you to request for help for an app purchased within the last 90 days.

  1. When prompted, enter the Apple ID and password used to initiate the purchase of the item, then click Sign In. 
  2. Find the item you're having a problem with, then click Report a Problem next to it. 
  3. From the Choose Problem menu, choose the issue you're having. 
  4. Follow the onscreen instructions. You might be asked to describe the problem in a text field. 
  5. Click Submit, and Apple Support will review your problem.

For more details click here to see How to get a refund from the App Store /iTunes

For further support  click here - iTunes Support for payments using App Store


Click here to see Steps to use restrictions to protect your App Store from unintentional or unauthorized purchases