I got a bill for AWS free trail

Hello.

First, delete the AWS service that is causing the bill.
By looking at your bill, you can see which AWS service features in which regions are being billed.
You will continue to be billed unless you delete the AWS service for which you are being billed.
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/getting-viewing-bill.html#accessing-your-monthly-charges

If you encounter unexpected charges, please contact AWS Support by opening a case under "Account and billing".
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/checklistforunwantedcharges.html

For questions about your AWS bills or to appeal your charges, contact AWS Support to address your inquiries immediately. To get help, see Getting help with your bills and payments. To understand your bills page contents, see Using the Bills page to understand your monthly charges and invoice.

By the way, even if you are using the free tier, the bill itself will be created. (You should have received a $0 invoice with no charges.)