I have the same situation. I mailed my I 539 to NSC and it was returned to me, then I mailed it to CSC, but then it was mailed back to me from NSC. I guess CSC transferred it to NSC. I tried to call but can't find someone to talk at all. So I just write a cover letter saying "this is the third time that I mailed my form I 539" blah blah and mailed it again to CSC. One week later, I got a receipt notice, "WACxxxx". I guess yours will be fine too.