Login to the Admin Portal https://portal.duocircle.com>> Click My Services >> click your SMTP service.
The service details page will display your current SMTP username, the number of credits on your account (in multiples of 150). You'll be able to check the number of emails sent, and also the number of email credits remaining.
The SMTP credits reset each day at 0:00 GMT.
You can also update your password or add more credits via the page.