When you signed up for the free trial, you saw the subscription price along with the message that you will be charged if the trial is not cancelled at least 24 hours before the trial period ends. I appears that is exactly what happened and it makes no difference if you use the app or not. The same is true for any service, for example, if you have a Netflix subscription you will be charged each month whether you watch any of the shows or not. You did authorize it when you double clicked the side button with the amount showing on the screen, followed by verification with Face ID or your Passcode.
In most cases all transactions in the App Store are final, but at times Apple may provide a compassionate refund. It should never be expected though. You can try and request a refund using the link here, but you will not be able to request a refund for any Pending charge that has not been processed.
Request a refund for apps or content that you bought from Apple - Apple Support