I work for AA Insurance mate and we would definitely help with what we call uninsured driver protection. I believe Rothbury are a brokerage so they will have likely put your business through another company. I would chase them up again and just ask them to find out who he is insured with (you won't be able to do it yourself thanks to the privacy act). You could then call them to say you've been in an accident with one of their clients and put the ball in their/his court.