How do I make sure a subscription is cancelled

Use the following instructions to see your subscriptions: See or cancel your subscriptions - Apple Support

If there is no cancel option and it doesn't give a renews on date, that indicates that it has been cancelled.

Both of those things indicate that it is cancelled. If it wasn't there would be a cancel button and it would say that it renews (rather than ends) on 4/21/2021.

Also see the following from See or cancel your subscriptions - Apple Support

• • If you cancel, you can keep using the subscription until the next billing date.

in your iPhone go to settings>apple id> subscriptions. from there you wills see a list of all active subscriptions. If you cancelled a subscription but it still has remaining days during your paid free time... it will indicate that here as well.

Click here and follow the instructions.

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That is because the subscription will expire. You don't need to cancel it.

You shouldn't be billed. See FoxFifth's answer.