In the same boat, with nowhere to complain about it, and with all the gigs dusted from the search results, it's really a bit extreme :) I have no idea how to regain what I used to have.
It's clearly disappointing. There's no clear instruction on how to gain it back. Each time customer support provides the generic, long-explained things that don't even make sense. Yet, there's no clear way or time period of how to regain it if your success score is lowered to 4. I wish they could have given each seller a time period to adjust to the new system, instead of entirely wrecking what people have earned throughout the years.