If he actually feels he is being watched by the government, wi-fi, TV waves are talking to him, etc. those are classic symptoms of schizophrenia. That is not being different or rebellious...that is having the most severe mental illness that exists, untreated. Has he ever mentioned voices telling him things or seeing things that aren't there?
Even if he has a severe mental illness, you can only do so much. He has to get help. However, if my adult child had symptoms of schizophrenia, I would throw away the "you can do it yourself" rule and try to get him home and into a hospital. Medication and close outpatient therapy after the person is stablized is the only thing that helps schizophrenia or schizopaffective disorders. These are not drug addict symptoms. These are symptoms of somebody who may not know reality from fantasy. Yes, they can be mean, but it is because they feel you are against them, maybe poisining them with your vibes, etc.They also often use drugs to try to self-medicate, which does not help the issue at all. And, of course, if they 100% refuse to get help or to come home and let you take them for help, you can not legally force them to do so. Dumb law, in my opinion.
Are you sure he is not the way he is due to severe mental illness? I put that in a different category from those who deliberately fry their brains on drugs. In my opinion, they need a different sort of handling, no matter how old they are. I would help a 50 year old who was walking around the street, talking to herself. I'd probably call the police and tell them somebody seems to be lost and possibly sick and would not report them as criminal in any way. These are the homeless we hear about who are mentally ill without the right treatment, the 1/3 of those on the street who are not that aware of what they are doing, who may be paranoid and believe everyone is in a plot to get them because they have superior knowledge or powers. They are the sick menally ill, on the streets because we have shut down our hospitals that are supposed to help them get well (I'm not sure all of them did help, but at least they had a bed and meals and maybe electroshock therapy). So sad. I hurt for you and for him.