I'm being charged with no active EC2 instances

Do you have any instances that are stopped but not terminated? These will still be accruing a charge (only a few cents) for the EBS storage they are consuming. Snapshots are another thing to check, the storage space they consume is chargeable.

Go to the billing dashboard https://console.aws.amazon.com/billing/home and click Bills on the left hand pane. Go down to the foot of the page that opens up on the right and you can see what you're currently being charged for. Expand the Elastic Compute Cloud section to see which regions have EC2 resources in them, then you can find these in the console and delete them.

• If you have purchased Reserved Instances, these are billed regardless of whether or not you have any active instances. Reserved Instances are billing features and not physical instances.
• If you're not currently using an Elastic IP address that you have reserved, you may still be charged for it.
• AWS charges for data transfer under certain conditions, such as data transferred out of AWS to the internet or between regions and Availability Zones.
• If you've deleted an EC2 instance but haven't deleted the attached EBS volume, you could still be charged for the EBS volume.
• Snapshots of your EBS volumes are billed separately and could be a source of unexpected charges.
• Elastic Load Balancers (ELB) are billed separately from EC2 instances and could be a source of charges.

I suggest you dig deeper into your AWS Cost Explorer and Usage reports to identify the exact services for which you are being charged. You can filter your AWS costs by service in the AWS Cost Explorer.

Also please check the following post. it may answer your problem

https://repost.aws/knowledge-center/ec2-billing-terminated