Managing auto-renewing subscriptions -
http://support.apple.com/kb/HT4098
ASC - Late 2012 Mac mini, macOS 10.12.4; Watch, 38 mm silver AL, watchOS 3.2; iPad Air 2 & iPhone 7+, iOS 10.3.1; TV 4th Gen, tvOS 10.2; Airport Express
Managing auto-renewing subscriptions -
http://support.apple.com/kb/HT4098
ASC - Late 2012 Mac mini, macOS 10.12.4; Watch, 38 mm silver AL, watchOS 3.2; iPad Air 2 & iPhone 7+, iOS 10.3.1; TV 4th Gen, tvOS 10.2; Airport Express
Did you trial anything and not notice the terms of the trial?
On the invoice is a section marked 'Report a problem'. Report this as your problem and explain as you have in your post and ask them for a refund. They will tell you why it was charged and advise if they can refund or not.
Invoice for Apple Music Membership