Dispute with hk property agency what to do?!? Iam lost

I am in dispute with a real estate agency hong kong
They pretended a shortfall due to the cancellation of the lease of real property
They require half my deposit
While I have not signed a contract defining their commissions
What should I do??
Are there competent and free legal advice service in a 1st time
Or what are the administrative procedures to make by itself ??
Any advice welcome
Thank you

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