You may be right that he is in error, but be careful not to write someone off as beyond redemption. God saved far worse than any of us. Present the Scriptures, warn him if necessary, and leave the results to God. Be at peace my friend.He cannot be redeemed, been trying for a long time he wont change, has a hart of stone, go at it if you can.
He claims to have the holy spirit yet REFUSES to obey Christ, thinks he does not have to follow His Commandments, he is toast until he repents ans does God's will.
He wasted a lot of my time don't let him do this to you as well.