Someone is using my Apple Account and I can’t play music

Yes, you go to Settings > [name on top] and scroll to the bottom. Any device listed there is one signed into your account where you will not be able to play simultaneous music. If there is a device that is not yours, tap on it to delete it and change your Apple Account password, so they cannot sign in again.

Change your Apple Account password - Apple Support

Then go straight to changing your Apple Account password. Anyone that is using your Apple Music will no longer be able to do it.

Also, note in the screenshot I provided, there is an item called Media & Purchases. This is the account used for Apple Music and in most cases it is the same as your main Apple Account on the top of the page, but if there is a different Apple Account seen under Media & Purchases, that is the Apple Account that you and/or someone else would be using for Apple Music. You can check the device list for that Apple Account by going to account.apple.com and signing into the account you see at Media & Purchases, then choose the Devices option.

Sorry, you are not in the correct location.

• Tap the Settings app
• Tap your name on top
• Scroll down to see the list of devices that are signed into your account.

You will see a list of devices like this:

Do these reports happen in one place, or everywhere you go and everywhere you try listening?

If only in one place, how complex is your local network?