Sometimes it take weeks Google to reply (which means some how Google doesn't receive our e-mails quick as we think) I know that because it has happened to me before. Earlier if you try to contact Google by e-mail try this time by making a call to them.
It could be that an external site is promoting your site or a specific page and that the ads are very relevant to the traffic. I've articles that achieve an average CTR of 55% per month and there is no problem with them. I found that if I changed the main ad panel from text only to text and image that some clicks increase in vale by 66%. As long as you have contacted Google to cover your back you might make this change if you haven't already. Also, the clicks aren't added to your account in real time and if google found them suspicious you wouldn't be seeing any income from them. Also, I don't reckon bots click ads (could be wrong)...
I got email from adsense couple days ago about invalid clicks, same email that you got. And they disabled my account for invalid clicks. But I didn't do them, I think it is my friends or some family members tried to help me but they didn't know about invalid clicks thing, and I didn't now that they were doing it. So, now I know but it is too late. I wrote yesterday letter to google through this appeal form where I explained all situation, so I hope that they will hear me. But from what I read recently I see that my chances are not good. I spent like a month trying to figure out how all this adsense thing works, plus some time to put their code on all my pages. I made my website from scratch so website managing is not automatic like with WordPress tamplates. And after I set everything up, after three weeks they disabled my account. So, I am kind of pissed that I lost my time with them. Now if they will not reopen my account I have to go through all my pages (~50) and delete all their code. They are like Gods, they can disable your account even without explanation. They don't care how you got those clicks. So, now I still have small hope that they will reopen my account again, but in the main time I am looking some other ways how to put ads on my website. AdBrite doesn't look too bad. So, if google will not answer I will go with adbrite. Maybe you have to start doing the same. Have some hope for google but don't waste time while you are waiting. Try to find some other ways. I found so far like 5-7 website which provide this type of service. It is depend which one fits more for your needs. P.S. Sorry for my mistakes, English is my second language.
Now, be honest, did you ask them or at least told them that you were making money when people clicked on those ads? Yes, you are. Probably you'll have to because It's 99% unlikely that they'll reopen your account. "The last thing you lose is hope" says the adage, but be realistic: that they'll reactivate your account is way too unlikely. If you have decent traffic, why don't you sell ads by your own instead of using an advertising network? Adbrite pays almost nothing.
Well, even though my site is providing useful and interesting information it is still new (a month old), and I don't have a lot of traffic yet. So, I don't think that somebody will want to buy space on my website now. But I am sure later they will. That is when I will start working with those services like BuySellAds. For now I thought that I could make couple cents with adsense. Well, maybe next time. Yea, I know, but like you said "The last thing you lose is hope" )