I don’t think impersonating a committee member is a crime, or even an offence under strata law, unless he is doing it for financial gain.
However, there could be a strong argument that this is a form of harassment against all the residents of the building and you might consider seeking an Apprehended Personal Violence Order.
At the very least, it would be worth talking to your local police about them having a word, and telling the ex-committee member to pull his head in.