Billing inquiry

Here's a re:Post article that you might find helpful, it has information to assist with making sure that you don't incur charges while using Free Tier.

Also, it's possible that you might have active resources that you're unaware of, here's how you can check.

You can also use the cost explorer service to check what services are generating charges.

you can also open a billing case through your account. Please choose Account and billing, so that the Billing team can look at this specific case and provide a resolution.