Famous™ said:
Ring a drug help line thingy, i forgot what it's exactly called, google it, it's for people who want to help their friends and family
Greatest-advice-ever. NOT! Look at the way you even said it? "thingy" did you read the OP? OP already said that his father went to rehab multiple times,and just quit.
OP,you can't help your father,your father is the only one who can help himself. But somebody in his eyesight gotta show him he can. So go make a plan to show him,you're fucking done with it,and that he will regret his choices. Goodluck in this hard time!