My S7 is stuck on android 6.0.1

[Android Central Question]

So recently I bought an unlocked s7 but it has refused to update at all. When I try to look for an update it just says that it is on the latest firmware. I believe that this comes from the fact that it is an at&t phone or maybe its something else. Aside from the problems updating everything is working well, and I've looked for a solution online but can't find anything. And I don't use at&t I use T-mobile so maybe that is it? Any help at all is welcome.

 

[chanchan05]

It needs an ATT sim inside it to update.