Apple Music

I recommend reading over this article as it goes over how to manage your subscriptions, report a problem, and handle your billing information right from your devices, that way you can cancel the duplicate subscription if listed: Billing and Subscriptions.

To request a refund for the duplicate charge, please check out this link: Request a refund for apps or content that you bought from Apple

If the above steps didn't help fix/isolate your issue, I recommend to reach out to Apple Support here: Get Support