As mentioned you want to cancel the plan and request a refund. A refund depends on when you cancel and the type of subscription you purchased. For most plans, you get a full refund if you cancel within 14 days of your initial purchase.
For IOS Apple manages the Acrobat Reader premium subscription purchased from the Apple App Store. Refund purchase For Android. Google manages the Acrobat Reader premium subscription purchased from Google Play Store. You can cancel your subscription using the Google Play Store app on your Android devices. Refund Purchase