Account and Billing Support.

I understand your concern about the unexplained decrease in your AWS credit balance. This can be frustrating when you can't see where your credits are being used.

To understand where your credits are being consumed:

1. Check your AWS Billing Dashboard, which should show exactly which resources are generating charges. Sometimes credits are being used but may not immediately appear in the credits page.

2. Look in the Billing and Cost Management console:

• Sign in to the AWS Management Console
• Open the AWS Billing console
• In the navigation pane, choose "Bills"
• Look for "Total Discounts" under the "Credits, Total Discounts and Tax Invoices" section

3. Try viewing your credit usage in Cost Explorer:

• Open Cost Explorer
• Go to Reports
• Use the "Monthly cost by service" report
• In the right menu options, select Dimension = Cost Category
• Then select Charge Type = Credit

4. Check for resources that might be consuming credits without your awareness:

• NAT Gateways (these are not included in Free Tier and can be expensive)
• EC2 instances larger than Free Tier eligible types
• Resources running in multiple regions
• Elastic IP addresses not attached to running instances
• Stopped (but not terminated) EC2 instances that still incur charges for EBS volumes

If after these steps you still can't locate where your credits are being used, I recommend contacting AWS Support directly as they can provide account-specific details about your credit usage.
Sources
Billing AWS Free Trial 120$ | AWS re:Post
Can't see credits in my credits page | AWS re:Post
Hight cost of AWS | AWS re:Post