Please write in a support ticket through the in-game Contact Support button. One of our CS agents will take care of you.
Note: Contact Support can be found by going to the Main Menu->More...->Help.
A screenshot of your emailed receipt should be fine. Please note that it must clearly show the date, package purchased, order number and account ID/Google Email.
If you did multiple purchases on the same day as your missing purchase, please also include a screenshot of your purchase history.
For Apple, that can be accessed through the steps detailed here:
http://support.apple.com/kb/HT2727
For Google Wallet, please provide the email you use to make purchases with and the purchase history as found through the steps detailed here:
https://support.google.com/googlepla.../2850369?hl=en.