Hi @Mon0497 , I'm sorry you've had bad experiences that have led you to complaining, or wanting to atleast. I'm in the same position at the moment and will be complaining myself about a "professional" I have dealt with (MH Nurse).
You can complain to the HCC (Health Complaints Comissioner), MHCC (Mental Health Complaints Comissioner) and/or APHRA (Australian Health Practioner Regulation Agency). You can also see if someone who is treating you or another person is registered on APHRA (some may not come up but that may not mean that they're not registered, I don't know). As far as I know anyway, I'm not sure if there's any others.
You can also go to your complaints/liason departments at hospitals, clinics, etc. or complain online or by paper/writing if they have one.
Best of luck, I hope you have a good outcome.