Greetings,
If all forms of communication fail and you need to go "legal" I can suggest to you this company
http://www.didntpay.com.au/.
Basically they provide an easy to use service where you register the debt online. It then sends the person an email giving them 7 days to pay before further action is taken. Thereafter, if they don't pay it registers the company as in default. Interestingly, if another party uses google to then search for this company,it comes up as owing you money. A pretty good reason for them to pay you to have this removed!
In a way its pretty harsh, so I would exhaust all other avenues first!
Kind regards,
Nevenka Sheridan