How to be sure billing fixed

1, Not sure what actions you have taken but as long as you deleted the resources that cause the billing, it would stop. If you need specific guidance, you should clarify what components you are trying to clean up;

2, you can setup alert or keep monitoring the billing to make sure you have indeed properly terminated the resources responsible for the bills;

3, if you no longer need the account, you can shut it down.

Go to cost explorer and check daily view.