I just realized u mentioned that also. Thats very strange that an interview for the i751 is scheduled a day after your n400 as initial and that you already attended your initial interview. Something isnt right. If anything it should be a combination interview. I would contact the call center and request tier 2. Tell them that you were scheduled for the first interview and attended it last year and then you are in receipt of another letter advising of an initial interview scheduled a day after your n400 interview. My i-751 was last year in october, they actually "cancelled" my interview but I went to the office two days prior to my cancelled interview to get the stamp and was told my interview was still on and they were expecting me. The system is messed up. I had email, notifications, the case status, and when I called in and spoke to regular rep they told me it was cancelled but when i got to the office it wasnt cancelled. Even afterwards they didnt know I had an interview on my cancelled date. I didnt get my greencard until January 2022. But yea, I would call the tier 2, perhaps see if you can do a case inquiry also that way you would be in touch with a representative out of that office. Detail your concerns. Keep us posted and good luck.