Apple has changed the rules for subscriptions. Previously, subscriptions were canceled by default if their cost increased, and users did not click in the pop-up notification that they agreed to pay more. However, now such explicit consent to automatic renewal is not required — although not in all cases.
As Apple points out, subscriptions will renew themselves if:
subscriptions become more expensive no more than once a year;
automatic renewal is allowed under local law;
monthly subscriptions become more expensive by no more than 50% or $5;
annual subscriptions become more expensive by no more than 50% or $50.
Users who want to unsubscribe will have to go to the app settings.