Do you mean the company is deregistered?
Someone must own the unit, either a person or a legal entity. If the company that owned it has been deregistered, it no longer exists. So you could assume that the unit has been transferred to another person or legal entity.
Add into the mix that under strata law, a proxy cannot have effect for more than 12 months or 2 consecutive AGMs, whichever is the greater. That is, a proxy has to be refreshed.
If the company went out of existence some time ago, then the proxy wasn’t valid for both reasons.
I would say that you can challenge the by-law as not being valid.