Why was I charged during the Free Trial Period?

Did you cancel the trial subscription properly?

Managing auto-renewing subscriptions -

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

You might need to scroll down to find the Cancel Subscription button.

Scroll further down the link for instructions for non-Apple devices.

Things about subscriptions;

⁃ Deleting an app does not cancel the subscription.

⁃ A trial subscription must be canceled more than 24 hours before the renewal date or it may renew.

⁃ Many subscriptions are set to renew automatically until you cancel them.

⁃ If you see multiple subscription offers, as long as you don’t select one, the subscription shouldn’t renew.

⁃ If you don’t see Cancel Subscription, the subscription is canceled and won't renew.

⁃ An expiration date means the current subscription has been canceled but is available to use until that date.

⁃ Use Resubscribe/Renew if you change your mind about canceling the subscription.

Scroll to the bottom of the link for instructions for non-Apple devices.

If all else fails, check out Apple Subscription Support for articles and contact options;

https://getsupport.apple.com/?PGF=PGF63006&category_id=SC0060&symptom_id=23208

M1 Mac mini, macOS 14.6.1;  Watch, series 7 GPS/cellular, watchOS 10.6; iPhone 12 Pro, iOS 17.6.1; TV 4th Gen, tvOS 17.6; HomePods, audioOS 17.6 and Airport Express w/ Airplay 2

• Open the App Store on your iPhone
• Choose your Account in the upper right corner
• Choose Purchase History

What is the date for the purchase of this app?

That isn't what you were asked for. Post a screenshot of your purchase history that shows when the app was downloaded to your device.