Refund subscription for an app that changed in worse

I bought a subscription for Duolinguo but with the last update this app has become very bad and it isn't anymore what I paid for before. I canceled the subscription but I don't see why I have still to pay for the remaining 9 month for something that I won't use any more. And on the page to ask for a refund I can't ask a refund for it because it doesn't appear in the list of the purchases available for the refund. WHY? This is my first subscription by Apple but in the real world when you cancel a subscription you get refunded for what you won't use, this is how the real world is working! Why by Apple I have to pay for something that I won't use any more and above all because they changed they app to be worse!