Don't put serious scripts of your accounts on non serious websites. For demo purposes you didn't need to add Adsense on the sites, fake ads made by you would have done the job. Besides having little ROI in terms of AS those demo sites were not helping, they were a risk. We also know for sure based on experience that very often G might give wrong advice, and those automated messages can't be taken as a sign of "they knew and it was ok".
I'm on a similar boat, I develop my own CMS and have demo sites for my clients to see but everything on the demo sites is demo and don't include ads on them. I hope you get a way out of this within their policies and get your account working again.
Even serious demo sites with original content could be a risk if you add Adsense, the purpose of the demo site is to show it off to others, this way you are exposing your G Ads and your account on them. By experience we know that our websites with Adsense should be like the fight club, we don't tell or speak about it. Remember the threads of click fraud caused by friends that wanted to help once they knew the site was of a friend of theirs.