You can easily cancel your subscription:
iOS: Go to App in the Air > Profile > Settings > Manage Subscriptions > you will then be redirected to the iTunes app. Select App in the Air, and tap Cancel.
Another way for iOS: Settings of the Device > tap on your account > iTunes & App Store > tap your Apple ID at the top > View Apple ID Subscriptions > Select App in the Air from the list and tap cancel.
Only you can initiate the refund in the Apple ecosystem. Here is a guide https://support.apple.com/en-us/HT204084
Android: Go to the Play Store app > left menu > select Subscriptions > choose App in the Air > cancel subscription.
Refund: send to support team via feedback option on the app's settings your purchase ID (in the email from Google, starting from GPA..)
Samsung Galaxy Apps: you can make a refund here https://help.content.samsung.com/csseller/ticket/createQuestionTicket.do
We would like to hear why did you decided to cancel. To share your thoughts, contact our Support Team via feedback option in the app's settings. We would be happy to hear your feedback, and assist you if you have any questions or concerns.