Dealing with the matter in reverse order, you could dispute the result of votes at the AGM, but only if the disallowed vote would have made a difference. There is no “fruit of the poisoned tree” in this regard. Votes at the AGM are otherwise valid.
Should the strata manager have said you were “unfinancial”? If you owed money, yes. But since you didn’t actually owe the money it’s hard to fathom why they did this.
Actually, this is a very common form of financial bullying where committees tell the strata manager that they don’t think they should pay all or part of a bill like this and then the logical result is that you are rendered unfinancial.
In your situation, provided there are no other issues about who is responsible for what repairs, I would write to the strata manager and committee demanding that they withdraw the bill and issue a public apology, copied to all owners, admitting that they mishandled the situation.
If they refuse, take them to Fair Trading for mediation and report the strata manager to Fair Trading and the SCA (NSW) for misconduct and, in the case of SCA, breaching their code of conduct.