When the trial expires it automatically turns into a paid subscription. You now need to pay what you owe but you can try for a refund. First confirm you have canceled any subscription automatic renewal (if you simply delete an app this does not cancel subscriptions):
Review the information in this support article by clicking on the link to learn "How to cancel a subscription from Apple." - https://support.apple.com/HT202039
• "If you signed up for a free or discounted trial subscription and you don't want to renew it, cancel it at least 24 hours before the trial ends."
• An existing subscription will normally continue until the end of its term and may then renew automatically. Stopping automatic renewal is effectively canceling it. "If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew." The "Expires" date means the current subscription will just run until then.
• Read the link to see what to do about subscriptions that do not appear in your list.
• Canceling a subscription does not automatically start a refund. If you want to do that:
Click on this link to "Report A Problem" and ask for a refund. --> https://reportaproblem.apple.com/?s=6
"If the subscription that you want to cancel is not listed", click here --> https://support.apple.com/HT212052
If you still can't find a subscription, contact Apple Support using the link at the end of the support article.
If Report A Problem does not work for a subscription refund you may have to make a special request. Click here --> https://getsupport.apple.com/?caller=kbase&PGF=PGF51002&category_id=SC0060&symptom_id=23330
