We haven't yet received NVC case number after 4 months of NOA2 from CSC. Is this expecting? Should I visit CSC and ask why, what and how?

NOA2 expired already. What now? Extension letter? To whom?

Thanks for anything.

Have you called NVC to see what is going on: 603-334-0700, 1, 5

You can also call DOS: 202-663-1225, 1, 0 (I don't know if they can look you up with just your names or if they need the NVC case number)

I don't think you can visit CSC. But you can call them.