There is a process via Fair Trading for resolving disputes over rental bonds.
The following is from a Tenants Union factsheet:
At the end of the tenancy, fill in a ‘Claim for Refund of Bond Money’ form (from Fair Trading).
If you and the landlord/agent agree about the amount to be returned, sign the completed form and have the landlord/agent sign it … you can still make a claim if you disagree about the amount of bond to be returned to you. Fill in the form with the amount that you want paid. You do not need the landlord’s/agent’s signature. Return the form to Fair Trading.
Fair Trading will give the landlord/agent written notice that you have made a claim. If the landlord/agent does not dispute it, Fair Trading will pay your claim after 14 days.
If the landlord/agent does dispute your claim, they must apply to the NSW Civil and Administrative Tribunal (NCAT) within 14 days of receiving the notice and tell Fair Trading in writing that they have done so.
The Tribunal will decide how the bond will be paid out.