This probably means you're in the second string group. They will keep interviewing folks up to a certain point, and then back-fill any drops with your group. The back-fill typically happens for a lot of people around deposit deadlines. This sadly means you may not hear a "yes" or "no" until April or May. So don't despair, you're not out of the game. From what I understand, everybody in the second string group has gotten a spot for the last few years running. It's just unfortunate that acceptance comes a lot later than some would prefer.
When you call and ask for an update, just ask them when would be appropriate to follow up again. The admissions folks understand, and as long as you're polite and not calling every couple days, they won't frown on it.
This is a great school and is worth the wait. Keep your chin up!