How do I get a refund?

In most cases all transactions are final. For a charge on your device, it takes an explicit action by double clicking the side button with the amount showing on the screen, followed by authorization with FaceID/TouchID or Passcode. If you give anyone else your Passcode, you are authorizing them to use your device and that includes purchases. At times, Apple may provide a compassionate refund and you can try that here:

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

If you use Family Sharing with the Purchase Sharing option, you are authorizing Family Members to use your payment method for purchases. If you do not want family members to make purchases with Purchase Sharing, then you must use Screen Time restrictions to prevent purchases.

Don't share you Apple Account/Password with others, each person should be using their own Apple Account. To view and cancel any subscriptions you have, follow the steps here:

View or cancel app subscriptions on iPhone - Apple Support

Don't know what the reference to Eiffel is, for purchases on your device, it is the Passcode that authorizes those charges. Review the information provided to request a refund for an Apple purchase. Do you have those purchases listed in your Purchase History?

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

If not, then someone has gained access to your card and this most likely happened through a phishing message. For any fraudulent charge on your card, the solution is the same, and that is to dispute the charge with your bank.

If you think your Apple Account has been compromised, review the information provided here. It would also be beneficial to change your device Passcode.

If you think your Apple Account has been compromised - Apple Support