If the purchase was made via an Apple device then you will need to contact Apple directly. This link will take you to their contact page:

https://support.apple.com/contact 

If the purchase was made on Google, we can assist.  In order to search for the transaction we will need to see the GPA number, which can be found on the receipt emailed to you when a purchase is made.

If neither of these options are available, like in the case of fraudulent card use, your best option is contact your bank and Google or Apple to get any extra transaction information.  In those cases, we have no way to access the transaction to refund it from our end.