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.
Its been a long journey that started with completion of masters (F1) visa and today receiving green card (GC). I have been with Rajiv ji and his team since the beginning of my immigration journey (F1(OPT) -> H1 -> H1 Ext.-> Perm -> I140 -> I765 -> I485).
As said by everyone else here in the guestbook i also concur with all the things.
Firstly, they know what they are doing and are best at it. They have a solid knowledge about all the immigration rules, jargon, what can cause potential problem in future and how to handle the complexities a case has.
Secondly, very professional, prompt replies and free consultations. One thing that i liked is that they all are very easy to reach including Rajiv ji itself and that helps a lot in calming down the immigration anxieties of clients.
Best wishes to you and your team.