cancel amazon music subscription

If the subscription was acquired through Apple, click or tap > How to cancel a subscription from Apple - Apple Support

If not through Apple, you’ll have to cancel it through Amazon or however else the subscription was obtained

Follow the steps in the support document you posted from.

If the subscription does not show up when following those steps, then it is not tied to Apple ID you are using and you would need to either cancel it directly through Amazon's website ion it was started there, or through whatever other device it was started on.

See here: link-> https://www.amazon.com/gp/help/customer/display.html/ref=vnid_GCRZL3F2UZMNP3T3?nodeId=GCRZL3F2UZMNP3T3