Call him again, and if you get through, tell him to transfer the money electronically to your account, and for him to give you a reciept number for the transfer. if he claims he has sent the cheque already, tell him to cancell it and to transfer the cash, if he refuses or gives you excuses, you know without a doubt its time to play hardball.
In his defence though, VicRoads does make you hand the plates into them.