How to write a letter to the National Visa Center for not having the missing items they asked me?

My husband's case is at the National Visa Center and I already submitted everything they ask for, but for some odd reason I just receive a Checklist from them asking me for the same documents that I already submitted to them a month ago. I don't know what to do in that situation because the next process would have been the Interview letter, but without these missing documents they cannot sent me the interview letter. Please help me