Welcome to the world of AT&T updates! You are not alone. I spent the time to call AT&T CSR'S for about two weeks in December and got nothing but a run around. The competency is very low. I had one CSR finally admit that he could only help for billing / plan update questions. When asked why I was directed to him by AT&T's menu as Tech Support, he answered he didn't know.
Regarding updating via KIES, one can only update to 4.1.1. KIES doesn't recognize 4.1.2 and 4.3. If you are an AT&T customer, the only way to upgrade to 4.3 is by the OTA. Or you can go to XDA Developers and manually update. Just know what your doing if you take the XDA route.
I'm on 4.1.1 and have not received the OTA. Don't know of I'll ever get it. Right now, I have an out of warranty phone & rooting it & flashing roms is starting to seem a viable alternative.
Google your question. There's a lot of the same questions being asked & no answers from either AT&T and Samsung.