sma1488

It was a limited form of amnesty designed to garner votes for Democrats, at the expense of those going through the process legally.

How is it obvious? Do you know for a fact that he was not a qualified dependent last year?
Don't accuse anyone of tax fraud when you don't have any facts.
Signed,
Guy with a graduate tax degree

I would suggest to you that you stop thinking of this as "USCIS has screwed up". They sent you a letter saying that you had an interview in California. I know you tried, but obviously you didn't convince them to move the interview. Until you have something in writing saying it has been moved, you are responsible for showing up regardless of where it is. And it says right on the interview letter that a failure to appear means you've abandoned the process.
Now that you've gotten out of the mindset of "the government screwed up and I had no fault whatsoever", make an Infopass appointment and talk to a human being. Dress nice and be early for your appointment. Beg and plead your case. You did change your address, you made repeated attempts to change the appointment, etc. You want to obey the law and process. Ask them to please help you. Be contrite and apologetic, even if you are convinced they are wrong and you are right.
Or, spend money on an attorney and continue to be antagonistic. Your choice.
Regards,
Bill

I read the bolded part of the quoted post and thought it warranted some clarification, since many people reading the posts on these forums take every word to heart. Very few people who apply for the K-1 visa get denied. Requests for additional evidence or extra steps, yes, but not a flat-out denial. The vast majority in the end either end up getting the K-1 or petitioning for a different type of visa to bring their significant other to the US.
Waiting months on end is hard enough. No need to make people more pessimistic than is necessary