It generally takes a day or sometimes 2 to go from a Pending purchase to being Processed. The amount will show as deducted, but if there is a problem with finalizing the purchase, then you will see that amount returned to you balance. The same is true for any Credit/Debit purchase, where will it will show in your transaction history as Pending until it gets finalized.
If this has been longer than 3 days, I would contact Apple directly:
Contact Apple for support and service - Apple Support
Just so you are aware, refunds are not guaranteed and usually all sales are final. To prevent accidental purchases, you need to double click the side button with the amount showing on the screen, followed by verification with Face ID/Touch ID or Passcode. Some apps will offer free trials to evaluate if you find it useful, while others do not. If the app does not offer a free trial, refunds are not used to make every app a free trial.