These links may also be useful.
Subscriptions and Billing - Apple Support
View, change, or cancel your subscriptions - Apple Support
Get help with subscriptions not billed through Apple - Apple Support
Identifying legitimate emails from the iTunes Store - Apple Support
Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support
Get help with an item purchased from the App Store, iTunes Store, or iBooks Store - Apple Support
For payment/billing related questions remember on this forum you are not speaking to Apple but to members of the public much like you. If you are querying an authorised payment or want a refund you will need to speak to Apple directly.