What is apple.com/bill for $5.36?

If you want to confirm if the purchase was really made, log into your Apple ID/iTunes account directly and check your billing or purchase history. If there is an unauthorized purchase shown there, you can file for a refund from there using the Report a Problem form: 

https://reportaproblem.apple.com/

If you need to unsubscribe, follow these steps:

View, change, or cancel your subscriptions - Apple Support

Most likely something you, or someone else using your Apple account, purchased an item from the App Store that has a subscription. You'll need to find out what it is and cancel it.