How to talk to someone in billing.

To see what you've bought/subscribed to : See your purchase history in the App Store or iTunes Store - Apple Support and View, change, or cancel your subscriptions - Apple Support

If you want to talk to iTunes Support : http://www.apple.com/support/itunes/ww (click on your country's flag, the country where you live, and which is therefore the country on the account ; click on Contact Support towards the top right ; click on Get Help under 'Talk To Us’)

If you mean Apple Music (there is no 'iTunes music' subscription) : View, change, or cancel your subscriptions - Apple Support

There isn't a phone number for iTunes Support, if you want to contact them use the link I gave.