Holding an account

Closing your account might not automatically terminate all your active resources. You might continue to incur charges for some of your active resources even after you close your account. You're charged for any usage fees incurred before closure. You can look into https://aws.amazon.com/premiumsupport/knowledge-center/terminate-resources-account-closure/ which helps to find on how do you terminate active resources that are no longer need on your AWS account.

You can also check for active resources that you no longer need on your AWS account using instructions in here https://aws.amazon.com/premiumsupport/knowledge-center/check-for-active-resources/

Also it would be good idea to use AWS Budgets to monitor your Free Tier usage https://aws.amazon.com/premiumsupport/knowledge-center/free-tier-charges/

Not sure what kind of apps and services you have but yes if you don't need it, ensure to stop the services or release resources (if you can re-create it without impacting your application). Above links provide a good idea.

Lastly, this is a good reference https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/checklistforunwantedcharges.html to review.