Was in a similar situation
Dont wait till the 30 days as the uscis website tells you. If you or your attorney hasnt received in 7-10 days, call NSC and tell them that you have verified with postoffice/postman and leasing office. They will resend you one.
If they are not willing, hang up and call once again.
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Process to contact NSC Officer:
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1-800-375-5283
option 1-2-6-1
enter your LIN# and press 1 for correct
then enter option 3 then 4 it will take you to NSC office/officer