As you’ve stated that the mould has developed during the recent cold weather, I’ll assume that it’s presence or likelihood wasn’t noted on your incoming Condition Report.
That being the case, your Landlord has to maintain their premises in “reasonable repair” (NSW Residential Tenancies Act), and whilst you must ensure that you do nothing to make the situation worse, that doesn’t extend to operating a dehumidifier!
You have a couple of choices.
The first is to end your tenancy, and the second is to again approach your Landlord via the Property Manager (Rental Agent), this time in writing to politely demand that they commence the repairs identified by the building inspectors within a reasonable timeframe; say 7 days given the time that the issue has been known to them.
Keep records of everything written and stated verbally, because if nothing positive occurs within your requested timeframe, your next action (in NSW) is to seek Orders from the Consumer, Trader, and Tenancy Tribunal compelling your Landlord to make the repairs.
IF it comes to that, I advise you to first contact your local State/Territory Tenants’ Advisory/Advocacy Group; 02 9698 5975 in Sydney or http://www.tenants.org.au Statewide.