From Portal:
First of all, check the public virtual interfaces under direct connect service
1. Login to the AWS Management Console.
2. Select direct connect service and go to virtual interfaces tab
3. Verify if any public virtual interface is associated with any RDS databases.
4. Make sure to fix the configuration to avoid public internet routing through your direct connect interfaces.

References:
1. https://docs.aws.amazon.com/directconnect/latest/UserGuide/WorkingWithVirtualInterfaces.html
2. For creating private virtual interface: https://docs.aws.amazon.com/directconnect/latest/UserGuide/create-vif.html