It sounds like you have to issues here. To me it is also soundling like you have two Apple accounts. If this is the case then you need to be signed into the account that has the Apple Music subscription in order to be able to use it.
For help with a "not valid" account you need to contact Apple. Click here --> Choose your country or region - Official Apple Support Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service by telephone --> Contact Apple for support and service - Apple Support
This support article explains how to cancel a subscription from Apple on an Apple mobile device, Mac, PC, and online ➔ If you want to cancel a subscription from Apple - Apple Support , or this video will only tell you how to do it on an iPhone ➔ https://www.youtube.com/watch/XXx-J-ueCtE
Notes:
• You might need to scroll down to find the Cancel Subscription button.
• If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew. An "Expires" date (instead of "Renews") means the current subscription will just run until then. "Resubscribe" is just in case you change your mind about having it end.
• Deleting an app does not cancel a subscription.
• If you don’t cancel trials more than 24 hours before your renewal date, your subscription might renew.
• If you don't have an Apple device, see the options near the bottom of the support document.
• Many subscriptions are set to renew automatically until you intentionally cancel them.
You will need to be signed into the account that actually has the subscription in order to be able to cancel it.