Hello kerstin86,
To help us better assist you, can you let us know more about the issue you're experiencing? For example, do you receive an error when trying to access Apple Music, or something else? If you do get an error, what does the error say?
The above details will help us determine how to proceed.
If you need to connect Apple subscriptions from your wireless carrier to your Apple ID, please check out this link, which outlines that process and may help: Connect Apple subscriptions from your wireless carrier to your Apple ID
How to connect an Apple subscription to your Apple ID
1. Your carrier will send you a text message with a link to connect your subscription. Learn what to do if you don’t receive a text from your wireless carrier.
2. Open the text message and tap the link.
3. Follow the onscreen steps to sign in with your Apple ID and connect your subscription. If you see a message that says "This subscription is already being used with a different Apple ID," contact Apple Support to unlink your Apple ID.
If you have a Dual SIM phone, you can connect your Apple subscription on your default line.
Thanks!