Delete AWS Backup Service

The difference between snapshot policies and AWS Backup plans lies in their functionality and management approach:

1. Snapshot policies are specific to certain services (like EBS volumes) and manage snapshots directly within that service.

2. AWS Backup is a more comprehensive, centralized backup service that can manage backups for multiple AWS services, including ECS volumes, in one place.

Regarding your situation:

1. Having both snapshot policies and AWS Backup plans for the same resources is redundant and can lead to unnecessary costs.

2. The inability to delete the AWS Backup plan, even from the root account, is unusual and suggests there might be an issue with permissions or the deletion process. Here are some steps to troubleshoot:

a. Ensure all associated resource assignments (selections) have been deleted from the backup plan. You cannot delete a backup plan until all its resource assignments are removed.

b. Check if the backup plan was created by an AWS Organizations backup policy. If so, it appears as an immutable plan in the AWS Backup console and cannot be deleted directly from the account.

c. Verify that your IAM role has the necessary permissions, including "iam:CreateServiceLinkedRole" action, which is sometimes required for deletion operations.

d. If the issue persists, you may need to wait 2-3 days and try again, as there can sometimes be a delay in processing deletion requests.

Remember, deleting a backup plan does not automatically delete the existing backups. If you want to remove the backups as well, you'll need to delete them separately from the backup vault.

If you continue to experience issues, it's advisable to contact AWS Support for further assistance, as they can provide more specific guidance based on your account's configuration.
Sources
Delete a backup plan - AWS Backup
Backup deletion - AWS Backup
Backup plans - AWS Backup
Backup policies - AWS Organizations

Along with the recommendation above verify if the associated vault has any type of vault lock configured. This can prevent the deletion of recovery points as well. https://docs.aws.amazon.com/aws-backup/latest/devguide/vault-lock.html