After you make a purchase through the App Store, a confirmation email with your order information is sent to the Apple ID account you used when making a purchase. If you did not receive an email, you will find instructions on how to check your Apple purchase history here: http://support.apple.com/kb/HT2727

If you need to contact us for a purchase issue, please attach a screenshot of your Apple receipt and make sure the name of the purchased item(s) and date of purchase are visible.

You can find instructions on how to take a screenshot here: https://support.apple.com/en-us/HT200289