Hi Prashok (or Teutonic ... yes, I was surprised at first when I saw your new name

)
I sent my preferences to Ox on the very day I received the invitation, and, after I waited patiently for 3 business days, still got nothing. Then I started to worry and sent another email (on Thursday last week), explaining that I was worrying that my previous one was lost. I got a reply almost immediately, and the Adcom said that they received my first letter, but were still working on arranging the interview date and time (I asked for 28 Nov, in person). Later that day I received confirmation that my date was approved.
So it seems they had too many applications for R1, and now experience some problems sorting our preferences. But if you did not receive anything for more than a week after your initial email, I think you could write them again. Who knows, maybe your email was lost or something.
~
Greenoak