I don't use any of 'EC2 instance', why do I pay?

Hello.
Have you verified that all resources are not left?
Also, have you checked your bill to see which services you are being charged for?
If you are able to identify which AWS service is being charged for by checking your bill, delete or stop the service.
Active AWS services can be verified by following the steps in the following document.
https://repost.aws/knowledge-center/check-for-active-resources