From USCIS: Recently USCIS erroneously scheduled some customers for more than one Application Support Center (ASC) biometric appointment (Form I-797C).
you have already attended an ASC biometric appointment, and received a
second appointment notice for the same application type, please call the
National Customer Service Center at 1-800-375-5283 (TTY for hearing
impaired: 1-800-767-1833) to confirm that you do not need to return to
the ASC to have biometrics collected again.
If you have not yet
attended your ASC appointment and received more than one ASC appointment
notice, you should attend just one appointment and take both ASC
notices to that appointment.
USCIS regret the inconvenience and thank you in advance for your patience as they address the issue.