How to help son with his 'voices' and medicine

My son is on 400 mg of Seroquel and 20 mg of olanzapine for a couple of months. He still hears voices every day. He tells us whether they are high, medium or low. It seems like there are more days now when they are low compared to before. There’s definitely less paranoid ideation. No comparison to what it was like when he was incorrectly diagnosed as being bipolar and on the wrong drugs.