If you want to cancel your subscription, purchased via AppStore or Google Play, you have to handle that on your own in these stores. If you purchase subscription in browser via Fastspring, you can access your subscription management here on this link https://windy.onfastspring.com/account
UPDATE: I checked your account and your purchase was made in AppStore.
Also deletion of account doesn't cancel the subscription and you don't have to pay next periods, if you cancel it now.