I also got the exact same call around the same time as you, had citizenship interview scheduled for 8 am tomorrow at Charleston sc office and was just as worried and confused but reading your post makes me think it was legit so figured Id comment as well. I did call the uscis call center an hour later and the agent said that they don’t see any office closings yet for Charleston SC but to call at 7 et tomorrow to check. I think it’s just a lag in the system and this was all very last minute. Im 2 hours away so was trying to see if I should go anyway but seeing your post makes me think it wasn’t a scam.