Deleting an app does not automatically cancel a subscription. The first thing you need to determine is whether the purchase was made in app where it is managed by Apple or if you made the subscription with them directly. Cancelling a subscription managed by Apple is done here:
If you want to cancel a subscription from Apple - Apple Support
If it is not managed by Apple, you will need to contact the company/website directly to cancel the subscription. If you are unable to resolve the problem with the company, then the last resort is to dispute the charge with the payment method that was used. Contacting the bank used by your card will be essential. Mastercard, VISA, American Express, and Discover have a feature that will automatically transfer your subscription to a new card even if you cancel your current card.
https://paymentcloudinc.com/blog/account-updater/