The diagnosis may not be depression
what seems from your description
It may be a psychotic illness or schizophrenic illness who are known to not to take medicine and stop taking food from others because of suspiciousness etc.
he has to be supervised for his medication by someone who is staying with him
In european countries many NGOs or social services or suicidal help line do take care of such problems
It is a psychiatric emergency and intervention is highly important without delay