If you were in the ACT, what you describe would be ‘an absentee vote’, which is quite distinct from appointing a proxy to vote on your behalf. Our strata Act provides for both. Could it be that your ‘proxy’ appointment form actually functions as an absentee voting form if there is no person named as proxy?
I would check with the strata manager that they agree with the advice you received from Fair Trading. If so, you could go ahead with your intended absentee vote in expectation that the manager will advise the chair of the meeting that yours is a valid vote, should that be necessary.