Billing problems

You can find out the reason by reviewing your purchase history.

1. Go to reportaproblem.apple.com.
2. Sign in with your Apple ID and password.
3. A list of your recent purchases appears. If you’re not sure what you were charged for but you know the amount of the charge, search for the amount. 

See the link below for more info.

View your purchase history for the App Store, iTunes Store, and other Apple media services - Apple Support (CA)

Hope this helps.