Charges for directory service

Open a billing support case. You don't need a support plan to get help with billing.
https://docs.aws.amazon.com/awsaccountbilling/latest/aboutv2/billing-get-answers.html#billing-support

I understand your concern about unexpected charges for AWS Directory Service. Unfortunately, AWS typically does not offer refunds for used services, even if the usage was unintended. However, there are a few things you can do to address this situation:

1. Check all AWS regions for any active Directory Service resources. Sometimes these can exist in regions you don't typically use or may have forgotten about.

2. Review your detailed billing information in the AWS Billing and Cost Management dashboard. This can help identify the specific Directory Services being charged.

3. If you find any directories you're not using, you can delete them to stop future charges. Make sure to follow AWS's proper deletion process to ensure all associated resources are removed.

4. Be aware that even if you've stopped using a directory, you may still be billed unless it's fully deleted. There might also be related components like snapshots or backups that continue to incur charges.

5. If you previously had an Amazon WorkDocs site without active users, AWS may have removed it in late 2023, causing associated Directory Service directories to start incurring charges.

To prevent future unexpected charges:

1. Set up AWS Budgets and billing alerts to notify you when you're approaching certain spending thresholds.

2. Regularly monitor your AWS usage and bills to catch any unexpected charges early.

3. Familiarize yourself with the AWS Free Tier limits and conditions to avoid unintended usage beyond the free offerings.

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If you're still unable to locate the source of the charges or need further assistance, it's recommended to contact AWS Support directly, in your Support Center. While refunds aren't guaranteed, they may be able to provide a more detailed explanation of the charges and potentially offer guidance or, in some cases, a one-time courtesy credit.
Sources
Why am I being billed for directory services? | AWS re:Post
Being Charged For Directory Services Since February | AWS re:Post
Aws charging me for services | AWS re:Post