Billing Enquiry

There are a few potential reasons why you might still be seeing charges for RDS Multi-AZ even after deactivating it:

1. Delayed billing updates: AWS billing can sometimes take a few days to fully reflect changes in resource usage. The charges you're seeing may be for usage that occurred before you deactivated Multi-AZ.

2. Snapshots or backups: Even after deactivating Multi-AZ, you may still have snapshots or automated backups that are incurring charges. These can persist after instance changes and continue to generate costs.

3. Reserved Instances: If you had any Reserved Instances for your RDS deployment, you might still be billed for those even after changing the configuration.

4. Lingering resources: There might be related components or resources that weren't fully removed when you deactivated Multi-AZ.

To address this:

1. Double-check your RDS console to ensure Multi-AZ is indeed deactivated for all instances.
2. Review and delete any unnecessary snapshots or backups.
3. Check for any Reserved Instances that may still be active.
4. Use the AWS Cost Explorer to get a detailed breakdown of your RDS charges, filtering by usage type and region to pinpoint the exact source of the costs.
5. Wait a few more days to see if the billing adjusts to reflect your recent changes.

If the charges persist or you need further clarification, it's recommended to contact AWS Support. They can provide a detailed analysis of your account charges and help identify any resources that might still be incurring costs.
Sources
Abnormal Billing from RDS | AWS re:Post
To stop RDS from billing | AWS re:Post
I don't have anything on my RDS, but it costs me every month. | AWS re:Post