Does my 7 year old have schitzifrenia and not ADHD & ODD

My 7 year old son has been diagnosed for the last 4 years with ADHD & ODD, while he definatly has ODD I question the ADHD and have told his doctors about his strange afflictions and the hearing of voices that tell him to do bad things and scream at him. He know we cannot hear it and he goes in a trance when he hears them (on a daily basis). He has extreme violent outbursts and yet he is the most charming and loving child out of my 3 boys.

I live in Australia and need to find a child Doctor that specialises in afflictions such as this that affect younger children as he is simply labelled and we are sent on our way at present. They have however placed him on anti phsycotics?? not sure if it is simpler to send people like us on our way with drugs.

My son is needs help..