My son's dad drinks excessively, smokes around him, tells him to curse at me, keeps him awake util morning.

He doesn't answer when I call to check up on my son, curses and talks bad about me infront of him. My son has told me his dad hits his girlfriend, he puts the kids to bed real late, around 1:00 a.m. My son is 4 yrs old, his dad just started looking for him to take him like the court order says because they garnished his taxes, but from what he has told me he only does it out of curiosity to have my kid and to get to me because he knows we are really close. I know my son is in a bad enviornment, I've seen drugs in his apartment before when he's made me pick him up, he lives 400 miles away. He smokes around my son and he has an upper respiratory problem w/beginning of asthma. He has also told me he was drinking when he was driving with my son to Houston. Legal aid doesn't want to help me because they are free of charge and they say I don't have actual proof of my argument that he puts my son in danger. What can I do to atleast get supervised visitation?