Follow these steps to cancel your subscription:

On the upper left corner of the Home Screen tap on the “Edoki Club” icon (cogwheel) and then tap on “Manage account”. Tap on “Manage account” once again and the app will redirect you to the Subscriptions section of the App Store.

Once there, tap on the icon of Jungle Math Challenge and then on Cancel Subscription

You may also manage your Apple subscriptions directly from a computer from the official Apple step-by-step guide.