The family of one of the LI serial killer's victims revealed yesterday that someone, very possibly the prostitute's killer, called and taunted the little sister of the late Melissa Barthelemy not three times, as previously reported, but six times. During the calls, the exact contents of which are not being released, the voice apparently taunted the girl with crude comments like "Do you know what your sister is doing? She's a whore." The last call was received in August. Unfortunately police were only able to trace the calls as far as midtown Manhattan.