You should get an email receipt to the email address associated with your Apple account.
The email will be from Apple and will say, "your receipt from Apple", and also show you what you purchased and the amounts of each purchase. Here is a screenshot of mine with some of the info blocked out for my own safety reasons.
I get these emails about a day or 2 after I have purchased items either at the App Store or from iTunes. Hope this helps. Have a good one and good day.