Hi, I'd like to help you with your question.
I am sorry you are in this situation. It is very stressful trying to care for someone who is refusing to help themselves.
It sounds like you have covered all the bases for trying to get him help. The advocate is correct, you cannot force him to have treatment. It is the law that allows patients to refuse treatment, even those with disabilities such as your uncle.
However, that does not mean you could not still try to work with him on the issue. You could also have his doctor speak to him, or someone else he trusts like a friend or other family member. Does he have a case manager or other mental health professional involved in his care? See if they will help.
Be gentle when bringing the topic up and present the good and bad to the situation. Speak about it briefly and then let it drop. Ask again at a later time. See if the consistency helps him understand that it is important to get treatment when he needs it.
I hope this has helped you,