Where do we report someone using multiple Y! accounts to spam members of our site?

This person goes by the name of "Melissa" and she/he has been suspended 10 times today for spamming our site. The address went from favourmk1@yahoo.com to favourmk10@yahoo.com. Every time we suspend her, she signs up under another Y! account. We can't suspend by IP address on our platform. It is with NING. Would Yahoo be able to remove this person by IP address? She/he/it is abusing the Yahoo! platform.