Cancel your automatic renewal:
Manage your Apple Music membership on your iPhone, iPad, iPod touch, Mac, PC, or Apple TV - https://support.apple.com/HT204939 - "Learn how to cancel your membership, change from an Individual to a Family or Student membership type, or join an existing Family Membership."
Contact Apple and tell them you need to cancel right now:
iTunes [Store] Support - Use this form for assistance with account and billing, code redemption, or purchase questions - https://ssl.apple.com/emea/support/itunes/contact.html