Refund for a cancelled subscription not received till date

The amount of time it takes depends on the payment method that was used:

• Store credit—It might take up to 48 hours to see the refund in your Apple Account balance.
• Mobile phone billing—It might take up to 60 days for the statement to show the refund. Processing time might be affected by your carrier. You can contact your carrier for an update.
• Credit and debit cards, Apple Pay, Apple Cash, and all other payment methods—It might take up to 30 days for the statement to show the refund. If you don't see the refund after 30 days, contact your financial institution.

Check the status of a refund for apps or content that you bought from Apple - Apple Support

Subscriptions will always automatically renew and you will need to cancel the subscription to avoid future charges. Simply not using the app will not automatically cancel the subscription to prevent it from being renewed. That is no different than any Streaming service you may sign up for to watch on TV. The subscription will remain and auto-renew whether you watch any of the shows or not. To cancel a subscription made in the App Store, make sure you follow the steps here:

If you want to cancel a subscription from Apple - Apple Support