My device settings are configured to AT&T even though it's not an AT&T device

There is nothing wrong with the settings and until you insert another valid SIM card from a major carrier, the phone will show settings for AT&T.  

she said MAJOR carrier.  That means Tmobile ATT or Verizon

@lizdance40: I am already using a different sim but nothing changed. Even the factory reset didn't work.

@Glimmerman76: Yeah,I got that. But right now I am staying out of US and using one of the major Indian Sim carriers. But why this would happen on a unlocked device ?

The us versions automatically switch carriers.

But not sure why my device is still stuck with AT&T. This is not allowing me to get the updates. It is still running on Android 9. Just disappointed happening this to a completely unlocked device :-( . Any suggestions to make the settings default will be really helpful and appreciated. 

You need it to auto switch to Verizon or T-Mobile.  But you need US Sims for those 

Okay so there is no way of getting this done with an Indian sim card? I thought some sort of reset or R&D will help me get rid of this. There is no way AT&T can reset from their end?

Nope.  You are not connected to AT&T, which is the only way to receive updates. 

I switched from att to tmobile and my phone is doing the same thing and I have the s23 ultra. I can't get updates either. My reads I have no internet connection even though my wifi is on. What can I do?