QLD Unable to get a Bond Refund

I have paid a bond to rent a market stall container the Business owner has stated in writing via email my bond will be refunded minus an administration fee ,as I was not able to proceed with the lease and the lease was terminated. This was sometime ago . I have sent regular emails,texts and phoned with no result. How can I proceed now ?
Thanks

Thanks so much. I was on the QCAT website and wasn’t sure which category my claim would fit into. Thanks