Cancel Amazon Music
How do I cancel my Amazon Music?
How do I cancel my Amazon Music?
That is an Amazon thing. You'd need to go here...
https://www.amazon.com/gp/help/customer/display.html?nodeId=GCRZL3F2UZMNP3T3
Note that it can be billed through iTunes -- they have in-app purchases in Amazon Music on the App Store
But as you noted it could also be billed directly by Amazon if they subscribed directly.
Cancel Amazon Music