We're sorry to hear you'd like to cancel your subscription, and we hope that you can give it another shot in the future!
To cancel your Premium subscription, please follow these steps:
Go to the Apple App Store or Google Play Store depending on if you are on iOS or Android
Tap on your Profile in the top right corner
Tap on Subscriptions
Tap on Ember and select "Cancel Subscription"
If this does not help, feel free to check out the following articles, directly from Apple/Google:
App Store: https://support.apple.com/en-us/HT202039
Google Play Store: https://support.google.com/googleplay/workflow/9827184?hl=en