I'm so sorry to hear you are having a bad experience and kudos to you for speaking out about it. First you need to confirm if they are indeed a realtor meaning a paying member of a realtor association. You can do that by searching for them at realtor.com. If they are member, I would start by calling the MA Association of Realtors on their customer service line at 800-725-6272. You can also file a complaint with the Division of Professional Licensure for the State of Massachusetts on their complaint line at 617-727-7406.
Best of luck.