Well, considering that there were over 2,000 registrations within the first six hours, there is a certain probability that they may have exhausted the initial room block over night.
If the web site says to contact the hotel it's probably best to email them or phone them up. Last year they were running a waiting list, and there's usually some reshuffling going on once the dust settles and when people share rooms with their friends some double reservations are usually freed up.
You can also check right here in
the room sharing board to see whether you can team up with someone else, or, penutimately check
this thread for alternative accomodation in the area. It doesn't hurt to book a fully refundable(!) room elsewhere, then cancel that one when you get a spot at the Estrel.