Finally after waiting in anticipation my interview letter is in the mail according to customer srvc. my online status was updated tooo.....i know i had a hard time when they kept saying my file was still at vermont service center. for months ...put i was persistent.....i wrote number of letters to service center, obudsman, director and called evey week for an update..it wasnt that hard to do.i strongly suggest you call and let them know that you are past the processing dates and the will put in an inquiry for you.........i think when you call them most of them talk to you like they are doing you a favour. I suggest you keep a strong voice and ask questions. everytime i called i got new info about my case. if someone got testy it never really bothered me (i cant help if they dont like their job). usually when i go to uscis alot of ppl also talk to you like that ....if you think ure incharge and informed you wont be so nervous and scared like they want you to be.... 
last time an io was suprised that i knew more than her about immigration hahaha it was funny coz she was annoyed....... 
last time an io was suprised that i knew more than her about immigration hahaha it was funny coz she was annoyed.......