Try signing into your account via iTunes on your mac or pc.
On the upper right hand side under "Quick Links" click on "Purchased new"
Or, you can go to Store > Sign In via menu bar.
After you sign in go back to Store > View my account(firstname.lastname@example.org)
When prompted enter your password for your apple id, then click on "view account."
Then once in "Account Information" scroll to "purchase history" then click on right hand side "see all"
Then you will be in your purchase history to view all your past purchases.
If your purchase is missing you may have to contact itunes support @ http://www.apple.com/support/itunes/contact/