I am a US citizen, had applied for my parents GC in October 2009. Mom underwent fingerprinting three times here, but did not get her AOS done in time. End of last year my father (who got his EAD and AOS smoothly) had emergency heary bypass here, and then they had to leave back for India for more tests. Mom left on AP. Subsequently I wrote a letter to NBC, MO to ask them to expedite my mothers case. Yesterday I received a letter stating that she has go to Philadelphia USCIS office next week for "Completion of application to register for Perm residence." Mom is in India now.
You need to contact USCIS customer service for guidance. Definitely put something down in writing that you are requesting a rescheduling. Maybe asking your Congressman's assistance is the best way to go for rescheduling.
Discussion Topics, Thursday, 20 June 2019:
FAQ: Impact on current H-1B if another H-1B is denied ||H-1B joining another employer while a transfer, extension or amendment is pending|| When does one become H-1B cap exempt - change of status/visa stamp? ||What to do when past immigration problems are causing a current visa denial? || Downgrading from EB-2 to EB-3 || Can priority dates be transferred between husband and wife? || Applying for green card while on student (F-1) visa.
Other: Transferring EB priority dates || I-485 delay || EB-5 travel || B-2 visa extension || Consequences of H-1B extension denial || EB-1C eligibility || Multiple H-1B transfers simultaneously || Travel on AC21 Advance Parole, etc.
Excellent customer service! Very thorough and prompt.