I want to cancel my subscription, but there is no cancellation.
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Question marked as
If you do not see the subscription here:
View or cancel app subscriptions on iPhone - Apple Support
Then it is not being managed by Apple and you have the subscription directly with the developer. It would also have to be cancelled with them. What is the name of the app you have the subscription with?
You can also review your Purchase History if it shows the subscription being purchased through Apple:
View your purchase history for the App Store and other Apple media services - Apple Support
Just because there is an app, does not mean that Apple manages the subscription. There are many apps, for example, Netflix, YouTube, and Walmart to name a few, that have their own subscriptions that are not managed by Apple.