I have the same situation. I have waited 21 days but that mail might never come in: 1. INS might input a wrong address in my notice. 2.US Postal sorting machine can send it to a wrong state/city/street#. 3.The Postal Carrier might have delivered it to a house next or close to mine and they discarded it as junk-mails.
As in any part of that world,the performance and quality of works at Governmental Agencies are so Great that I can not trust. Good Luck!