When you make a purchase in the Google Play Store, 

they will send you a receipt email with the order number on it.

All Google in-app payments are required to send a receipt email, and based on the order number, we can find out the details of the items you purchased, the purchase time, and whether they are properly given.

Therefore, it is strongly recommended that you do not delete the email.

You can also check your payment details on Pay.google.com and please try as below.

1) Go to Pay.google.com

2) See activity section

3) Select an order (To see Transaction ID)