iOS
If you'd like to cancel you subscription on iOS, you'll have to do it through app store. Here're the steps you have to follow:
Go to Profile tab in Hearty App
Click on Subscription button
Next, click on Manage Subscription
This will take you to the App Store, from there select Hearty App
Now you can click on Cancel Subscription to cancel it
For you convenience here's a video tutorial that outlines these steps: