Are you seeing this in your Purchase History?
View your purchase history for the App Store and other Apple media services - Apple Support
Are you an Organizer of a Family Sharing plan that uses Purchase Sharing? Members are then allowed to make purchases that will be billed to your payment method.
Do you see a subscription that is managed by Apple here where it can also be cancelled?
View or cancel app subscriptions on iPhone - Apple Support
Requesting a refund that appears in your Purchase History can be done here:
Request a refund for apps or content that you bought from Apple - Apple Support
If you do see a purchase in your Purchase History, that can only be made after double clicking the side button with the amount showing on the screen followed by verification with FaceID/TouchID or Passcode. Members of Purchase Sharing must do the same and you can view their purchases when viewing your purchase history. If you accepted a free trial, then on that Authorization Screen there is a message that says to avoid a subscription you must cancel at least a day before the trial ends. If you did not cancel, then you would be charged for the subscription just like it says.