There was no Galaxy Nexus from At&t...The updates come from Google.Did you get the phone from AT&T? If so, contact them. They control the updates.....
looking at screen in fast boot modeOP, you'll have to check if it's a yakju or takju variant. These are the true Google versions, and should recieve all updates directly from Google. The samsung galaxy Nexus versions sold in Canada (and possibly elsewhere) are Yakjuux and recieve updates through the carrier.
Mine was originally a yakjuux on Rogers (Canada) which I converted to Yakju. It has recieved several updates that I wouldn't have gotten if it was still stock.. Might be something to look into if you're still having trouble