Membership(Subscription) is managed by Google and Apple store, so please check the following website.

Apple:
1. Open Device Settings -> tap iTunes & App store
2. Tap Apple ID
3. Click View Apple ID (You might have to Login or use Touch ID)
4. Tap 'Subscription' and select subscription for the following game.
5. Tap 'Cancel Subscriotion' at the bottom of screen.
NOTE: Please refer to the following [HERE] for more information.

Android:
1. Go to [Play Store] and tap my subscriptions.
2. Choose the game that you subscribe.
3. Tap 'Cancel Subscription'.
NOTE: Please refer to the following [HERE] for more information.