Another tattoo artist ruined my son's tattoo

My son had a tattoo parlos artist do his tattoo, when it was done healing, one of the eyes was not completed and lighter in color from the rest of the tattoo, my son went back to this parlor, but this artist is no longer there, another artist went over his tattoo, and blacken the tattoo leaving it demonic (it is a religious tattoo) the owner stated because my son signed a contract, too bad sue him, what can I do, my son's 1st tattoo and from religious meaning to a demonic jesus?