Sorry to hear about your troubles on eBay. As Marc pointed out, unfortunately, this isn't an uncommon situation for eBay sellers.
Although, I must agree with Marc that it seems very bizzare that you would lose your PowerSeller or Top Rated status from just one neutral feedback?
If I were you, I would certainly be chasing up eBay and asking why your status was revoked.
Achieving PowerSeller or Top Rated status is a big achievement and one that you should be proud of! And while it's not harder to achieve and maintain these statuses on eBay now, compared to 3 years ago when you started out, you've clearly got some strong skills there so don't give up!
Keep pushing on eBay, and consider expanding onto some other marketplaces like Amazon or Bonanza or consider Link hidden: Login to view, the easiest way to get your own store up and running.