Q: i was asked for a trial to apple music for 3 months i accepted and they charged my account 15 dollars

Did the three-months free trial end already?

What does it say on your invoice this payment is for?

To resolve billing issues, you have to contact store support directly:

iTunes refunds, billing issues

https://www.apple.com/emea/support/itunes/contact.html

Is it an actual charge (you've received an emailed receipt and/or it shows on your account's purchase history ?), or is it just a temporary store holding charge (About payment card authorization holds in the iTunes Store - Apple Support) ? If it is a proper charge contact iTunes Support : http://reportaproblem.apple.com or use the 'contact us' link at the bottom right of every page on here

Contact iTunes Support as per one of the methods already given - we are fellow users, we can't potentially credit you