I was shared family subscription but I can’t use Apple Music why?

Contact iTunes Support for assistance. See the Apple Support articles below for contact information.   

iTunes Support – world wide   -

Apple Support schedule phone call     -

Billings and Subscriptions   -

If necessary, use Twitter or Messages.

Apple on Twitter

Messages chat with Apple

Whoever took out the Apple Music subscription may have gotten a subscription for one person instead of a family subscription.