Unknown charges

Hello.

Up to 250 hours per month are free.
I have not seen the exact invoice image, so I am not sure, but is it possible that the portion of the invoice that was used over 250 hours was incurred as a bill?
https://aws.amazon.com/sagemaker/pricing/?nc1=h_ls

250 hours of ml.t3.medium instance on Studio notebooks OR 250 hours of ml.t2 medium instance or ml.t3.medium instance on notebook instances

By the way, if you encounter unexpected charges, we recommend that you open a case with AWS Support under "Account and billing".
Inquiries under "Account and billing" can be made free of charge.
https://docs.aws.amazon.com/awssupport/latest/user/case-management.html
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 AWS Billing. To understand your bills page contents, see Using the Bills page to understand your monthly charges and invoice.