Rescheduling biometrics in US for citizenship application?

I need to reschedule my biometrics appointment because it was set for a date when I'm going to be out of town, even though I provided available dates as requested. Immediately after I received the email with the appointment letter for the bad date, I responded to UKNationalityAppointmentsUS and asked to reschedule. After several days went by without a response I sent another email yesterday, but still no answer. The appointment is set for early next week.

The appointment I need to reschedule is at an ACS location, but I assume the new appointment will have to be at a VFS location because of the switch at the end of July. None of the communications I’ve received about scheduling biometrics have said anything at all about this change -- they've only mentioned ACS.

Anyone have ideas about the most effective way to get through to someone? Thanks!