I'll disagree with you, in some part...
The company, with the advice of their lawyers, used the shareholders money to pay to conduct a PUBLIC meeting... and they apparently contracted with you to provide a public service for the shareholders, paid for by the shareholders, in relation to that PUBLIC event. It appears to me that they didn't have any right or authority to interfere, in the way they did, with the PUBLIC meeting they'd sponsored...
I'll have to look at California public meetings law... and I will.
My inexpert opinion at this point, based only on what I've heard, is that what occurred is clearly actionable...