I’m not sure what it is that you want to achieve as you suggest that the committee will rectify the problem at the next AGM.
If it’s just a matter of holding the committee members accountable, and allowing owners to understand what has occurred, perhaps a motion to the AGM calling on the owners corproation to censure the committee members, with an explanatory note attached outlining the issues concerned, would be enough.
Obviously, the committee may try to block this but, as politicians all over the world discover on a daily basis, it’s not the crime that gets you, it’s the cover-up.
Regarding having withdrawn the complaint at mediation, you can still proceed with action at NCAT simply by saying that the conditions of your withdrawal have nor been met. Or you can go again, saying you were misled and the problem has not been resolved.
But, without knowing all the details, I think that presenting a censure motion to the AGM, and having the same committee members vote it down or block it, may be the only trigger you need to reopen the case.