I did some research on this topic because my K1 petition is now being processed by the NVC. Go to this website. It is directly at the consulate in Guangzhou. It explains everything about how to contact them about your case.
http://guangzhou.usconsulate.gov/contactiv.htmlAlso, if you have a complaint about the person you've spoken to, you can fill out a form. The following information must be recorded when you do call:
1. The date and time of your call.
2. The name of the customer service representative with whom you speak.
3. The identifying information you gave about yourself.
They will retrieve your call with that person from their database and listen to the actual call, thereby rectifying any problem and to help train their staff to "better server you" !
I hope this helps.