Did this 3rd party unlock policy just change or something? I have a Lumia 920 that I unlocked without issue through third party (albeit a few months ago). AT&T wouldn't do it as it had a past balance. I'm told this is the way to do it through AT&T (I know some people who work there):
Significantly changed. It essentially eliminated the 3rd party unlocking ability, and locked down their own method by giving you ONE choice...an online form you submit, which they can reject for any reason (IE: my AT&T iPhone 5S was purchased outright with no contract, I submitted for it to be unlocked by AT&T, and they rejected it saying that I was "Too close to my upgrade date", and that I would need to wait another 14 days to submit again...when I asked one of the CSR's, explaining that I was well outside of the return period since this 5S was purchased on September 28th, they responded with "Our records show you've had two new 5S's activated since the 5S's release date, you will have to wait until October 27th in order to resubmit."
Essentially, I'm being held hostage because they only have one system of unlocking, and regardless of whether you bought a subsidized iPhone or a full retail iPhone, the 14 day window PER iPhone applies, and not congruently. And because they have no ability to override this (yeah right, lol), there was nothing they could do to expedite the unlock. In simple terms, they hold AT&T 5S's hostage for 14 days EACH.