cancellation of debiting

Deleting a subscription does NOT cancel a subscription. See the directions in this link to learn how to cancel a subscription --> How to cancel a subscription from Apple - Apple Support

You can request a refund, but that doesn't mean they will approve a refund --> Request a refund for apps or content that you bought from Apple - Apple Support

Unknown Charge?

1. App Purchase
   1. Curious about a Charge? --> If you see an 'itunes.com/bill' or an unfamiliar charge on your statement
   2. If you have an issue with an app on App Store or billing --> Request a refund for an App Store or iTunes Store
2. Subscriptions
   1. You may view a subscription to an app --> See or cancel your subscriptions - Apple Support
   2. You can also request a refund for a recent renewal of an in-app subscription purchase 

Avoid accidental purchases

1. If it is your device then, please --> Use Guided Access with iPhone, iPad, and iPod touch - Apple ... before handing over a device to a child.
2. If it is your child's device then in the future, enable the Ask to Buy feature --> Request and make purchases with Ask to Buy - Apple Support