You can unsubscribe anytime by logging in to your account, selecting the user icon on the top right, and going to "Account and Settings" > "My Subscription". Find the tier you’re subscribed to and click the “Unsubscribe” button below it.
If you registered using ApplePay, then unsubscribe by going to your iCloud settings by clicking your name in the settings app, and then selecting "Subscriptions". Find S&S under the active subscriptions list and click "Cancel Subscription".
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