OK, in a scheme of 20 units, each owner can only carry one proxy.
Your AGM was quorate – just – but even if it hadn’t been, the chair only needed to wait half an hour then declare that those in attendance constituted a quorum.
You need to organise yourself before the next AGM to make sure that you carry valid proxies with enough people turning up to elect a new committee.
You don’t need to foment revolution – just a quiet word here and there about how the building is being run, deteriorating standards, reducing values and excessive costs. That usually does the trick.
By the way, a committee of five may be too many for a scheme your size – especially when two people never turn up. Again, your next AGM should set the number of people on the committee (three would be adequate).