only your own senators and congressman

my 2cents:

write only to your own senators and your congressman/woman, but do follow up closely once you got reply from them. Talk to the one who actually worked on your case, and let him/her to follow with FBI (if NC). If he/she simply works with USCIS, you are just wasting your postage (and your big efforts too). So tell them requesting USCIS is useless, tell them do not bother about USCIS.