Subscription refund

Hello,

yesterday i subscribed to an app and I would like to cancel the subscription and get a refund. Trough the website reportaproblem.apple is not possible: when I select the option “I did not mean to sign up for a subscription” There is no service I can ask a refund for. If I select “right to withdraw”, I see the subscription but can’t select it for a refund. How can I proceed to request a refund?