Who, if anyone, does represent Chabad?”
No one “represents” Chabad. It has morphed from a traditional monolithic chassidus whose Rebbe exercised unchallenged leadership to a fragmented set of subgroups with a shared preference for Black Fedoras, a foundational focus on Tanya, kiruv and kabbalah but passionately different views on the Geulah and Z’man Moishiach. When you get away from Eastern Parkway and Detroit, the differences fade substantially.