I contacted AT&T. Was on phone with rep in US for 1 1/2 hours. He was in the process of running a test, got disconnected. So I called back. A different rep answered. She advised me that their Clarify and Intelligence systems were down. Apparently these are the internal names for their systems to track and to research issues across the network for the multitude of phones they have to support.
It was 3 AM EDT on Sunday at this point. So there was not much she could do, but to let the next rep when I call back to check these systems cause they were down for maintenance.
Called on Sunday around 2 PM. Another rep answered and couldn't find any info in the system. Wanted to know what was so important about Denim and didn't I get the update already. Told her this update has been released by MS for over 8 months now to AT&T and some have received it on their Lumia 635 circa June 2015, but others like myself have not. She didn't seem to be familiar all that much with Windows Lumia phones, which had me concerned. LOnce I explained the names, Lollipop for Android, she got the message, ha! ha!
She looked in the system, asked me a few more questions, had me take the battery out to check for a white strip that detects water damage. Then called me back.
At that time she advised me that based on her documentation, the only way to resolve the problem with the OS Version I have which is 8.1012397.895 (confirmed by the other rep as not being the latest), would be to replace the phone.
The other rep was going to see if he could find a way to push this OS Version out to me so that I would be on the correct OS Version and then receive the Denim update OTA (wireless). Really nice guy!
Well since my phone is still under warranty, she indicated they are sending me a new phone this week and I can return the current one I have with the box they will provide. That phone since it new, should have the latest OS Version, firmware and Denim update etc., but if not, then it should download automatically.
I will see in a few days. Had the phone been out of warranty, I don't know what they would have attempted, but I think the answer would have been - "Sorry, nothing we can do".
Just wanted to post my finding here so far to the others.
Will post again once I get the new phone to see what transpires.
The carriers just make this impossible.
I can only imagine what would have happened with the millions upon millions of iPhones that are out there, it Apple wasn't able to get all those phones firmware updates and security updates when needed. It would have been a total disaster for AT&T. I'm sure Apple would have taken the matter in their own hands, whether the carriers liked it or not.
Can't wait till Microsoft take a solid grip on the updates for their phones like they do for their operating systems. Maybe the new Surface Phones next year will allow the updates directly from MS, just like Windows 10 updates, since all their devices will be running on Windows 10 - one platform for all.