I got a room via ihotelier, but only 16-20 were available.
Phoned the Estrel to ask if this can be changed: yes, through the same site.
Tried it while on the phone: 15/21 is not available, but single days 22+23 still would be (without the 21, so no use).
Asked how this could be?
Got told, that there are still plenty rooms available, but the contingent to book through this site with this code is used, they have to assign additional rooms to them, will take a little.
So it seems, there was a block of rooms for the full date, some for 16-21, and some for 15-21.
The 15-21 is out, as are the few rooms for the full date, because someone booked e.g. arrival on Sunday.
But as only a few booked a later departure than 21, 22+23 are still available as single days.
This means: There are still rooms, and not only a few. But theay have to be assigned to the EF and to ihotelier to be available.
No Panic, use your towel.