it happened to me too a few years back, just as I was about to reach my $100 mark of the month, maybe 3 or 4 days from the end of the month, they gave me that crap and I lost everything at the time I had them on only 2 or 3 sites, I have since then moved and built a larger network of sites, have a new adsence account and everything is fine, but that crap can happen to anybody ... so I know what your feeling ...
Some devious rival sites may go on to your site and start clicking away on your ads just to get your account flagged. There's so many black hat methods that are being used these days and many of them you won't have control over. It sucks. Cheers
Try and write them a nice informative polite e-mail and see what kind of response you get. Don't hassle them though every day, that won't get your account back at all.
I doubt you will be able to get your account...I'm afraid once it's gone it's gone, except for very rare occasions. Write them a polite email to at least find out what happened to cause this
That sucks man, this seems to happen a lot for no apparent reason. But I'm sure they do have one, all you can do is move on and try another advertiser. You could also try opening another account, it couldn't hurt to try.