Refund for music

If you got a plan with a mobile provider (Verizon?) that included a 6 months free trial period, then follow their instruction and/or the instructions for bundled subscriptions from Apple (1st link below). Do not subscribe directly with Apple for that offer, as the mobile provider is making that offer instead.

About bundling Apple Music through mobile phone service providers - Apple Support

Link mobile account to Apple ID: https://applemusic.com/carrier

Verizon Unlimited Plan Users Get 6 Free Months - Verizon

See also About payment card authorization holds from the App Store or iTunes Store - Apple Support. Although the trial might be free Apple may still check the validity of your account details and that your account could support should you continue after the trial. It may be that, in fact, no actual withdrawal from your account has been made.

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View, change, or cancel your subscriptions - Apple Support