How do I stop unauthorized Simple premium deductions from my Apple Account?

Is this a website subscription from Simple? Those are not managed by Apple at all and are billing your card directly. They do not go through Apple Pay where Apple could block those charges. You would need to contact Simple to make sure your subscription was cancelled and inquire about any refund. If you are unsuccessful, then it will require disputing the charges with the bank of the issuing card.

If this was an in-app Purchase, then it is managed by Apple and you will see the charge here:

View your purchase history for the App Store and other Apple media services - Apple Support

And and can cancel any subscription here:

View or cancel app subscriptions on iPhone - Apple Support

Requesting a refund for in-app purchases managed by Apple can be done here:

Request a refund for apps or content that you bought from Apple - Apple Support

Do any or all the charges display when you review your recent purchases here,

https://reportaproblem.apple.com/

Charges display per item. Receipts or statements sent by Apple may display multiple items as a single purchase. Purchases generally are taxable and you must take that into consideration. 

If you need to request a refund, instructions are provided at the link below,

If you want to cancel a subscription from Apple - Apple Support

Request a refund for apps or content that you bought from Apple - Apple Support

If the items do not appear after reviewing the above articles and links, there is a high likely hood your credit card was compromised, the details used by the scammers to purchase goods and/or services from Apple. Apple will review requests for assistance from local law enforcement. Please report the fraud to your local police. Most likely the details were skimmed when the card was used at an ATM or chip inserted or swiped at a transaction terminal.

If additional assistance is required from Apple Support, please use the links below to contact Apple Support. If you’re in the US please call  1-800-MY-APPLE or outside the US, consult the support articles below.

Contact Apple for support and service - Apple Support

Live Chat with an Apple Advisor in Messages. 

Live Chat not available in all countries and regions.