What would you do if you've sent addictional information that the local uscis request and it has been almost 3 years haven't heard response from them. Came to their office and they say the case's still pending. I wonder if they denied or....? Should I send another letter to NE rather than local office?

I tried to check case status online but it says invalid #s

LIN*.......

Well, I'd say something is definitely not right about this case...I probably wouldn't contact NE, because if the file is at the district office I doubt the Service Center could be of any help. If the district office wouldn't be able to give me anything more than a mere "case still pending" after 3 years -which is ridiculous!-I'd probably look into involve my congressman to sort this out.
I'm not expert, just telling you what I'd do.
Good luck!

ETA: The case # is probably too old by now after 3 years, so I assume that is why it tells you it's invalid when you try to check online.

Also...just totally out of curiosity...why did you wait 3 years before trying to find out what was going on?