To see your purchase history, do the following:

ANDROID:
1. Go to payments.google.com, then sign into the correct Google account
2. Select Transactions to view the order history in the Play Store
3. Select a specific entry to view the invoice

AMAZON:
1. Go to Order History Reports in Your Account
2. Select the report type from the drop-down menu, then fill in the start date, end date, and report name
3. Click Request Report
4. When the report is complete, you'll receive an email notification