Other mistake: In the scene where John is in the apartment with the cat and Angela closes the door, John then says her name to get her to reopen the door. He says the wrong name, "Rachel" (the actress' name) instead of "Angela" (the character's name).
Stupidity: How would a devout catholic like Angela not believe in the devil, as she tells Constantine? Makes no sense.
Suggested correction: Some Christians don't believe in the literal personification of the Devil. They see him more as a metaphor for all human sins. So according to them, the Devil is not something to blame evil on. Everybody has God and the Devil in them.