I personally have difficulties reaching the admissions as well (sent two emails to the admissions email with no reply whatsoever). I would suggest either calling/emailing the Assistant Director of Admissions or the Administrative Assistant if you want to ask about your status. You could call them to ask about your application status and ask if they are receptive to a letter of interest and updates. I wouldn't bring up your NSUCOM acceptance though, and based on my own experience, update letter is unlikely to change your application status unless you've had several significant accomplishments.