Hi Nelly,
I would be interested to read other responses to your situation.
However this is my interpretation of the facts:
Common law contracts have four basic elements: offer, acceptance, consideration (for example, payment) and intention to create legal relations
You have clearly accepted an offer to move into the accommodation and from all the circumstances it appears that this has evoked an intention to create legal relations.
The only thing you haven't done is pay (consideration). However you did promise to pay. And presumably the person offering you the room has acted in reliance on that promise by, for example, taking down the ad and telling other enquirers that the room is no longer available. Therefore, even though you may not have a binding
legal contract, the person who advertised the room may have what is known as an "equitable" remedy. The law of equity
presumes done that which ought to be done.
On this basis, the person who advertised the room, might be able to claim money from you equivalent to his reasonable costs caused for example by his reliance on your promise.
So if I were you I would negotiate an amount to pay him out of goodwill to avoid further legal hassles. Is the deposit or one week of rent cheaper?
I'm not sure if there is tenancy law in Victoria which modifies the common law of contracts.
If you want, you can also call Consumer Affairs Victoria to see if they have any other suggestions.
Renting - Consumer Affairs Victoria