At what happened to your shares at that point?
If I'm reading between the lines of your lawyer, your shares were wiped out at the time of sale? I've heard of this happening often (dilution of the common happens frequently before an IPO, for example. You can see it in the S-1s.)
Your legal rights stem from the LLC; whatever you are entitled to will depend on the exact fate of that company.
Harsh but fair: this is as it should be. Ownership based on work/effort/invention rather than invested capital is contingent on that work continuing for a LONG period. Generally these arrangements have a cliff also - so if you leave in less than 12 months your ownership is drumrole nothing. This isn't true only with startups - look at inventors in other businesses... in exchange for an idea and sample they get 1% of the royalties, it's small because sales & marketing & production are more important than the invention
It's entirely possible you have a case, but your description sounds like the prototypical ex-founder nightmare. Based on pattern-matching, you may get some cash, but nowhere near what you're saying you're entitled to have.
There's a risk though, if you have any entrepreneurial aspirations you'll burn all your future potential with the lawsuit. VCs and potential co-founders will be very wary of dealing with someone who has taken this route.