Yep, followed what shipping protocols Nikon mentioned; sounds like it may be time for a follow up call to Nikon. I would try to be civil with them so they don't put your camera at the bottom of the repair list.
I registered my D750 with Nikon USA two months ago, I don't know if having it in their system helped speed things up or not.
Mine is registered too. I just absolutely despise incompetence. *shaking my head
I'm going to call Monday. according to their web site the work M-F.