Well first of all plan on moving, it's unfortunate but when you push further it may not be worth living there longer. You could contact one of the local TV investigative reporters to see if they'll do a story & possibly confront the landlord. You should consult an attorney familiar with elder law and/or housing law they can give you legal advice as to how to take this to the courts or may refer you to a local housing rights group. Even consider talking to clergy if you're religiously inclined. The biggest thing you'll need to do is document the heat situation. Get a thermometer & take pics with the daily newspaper next to it 2-3x per day (morning, noon & night) to show a pattern of this. Courts and housing groups need proof more than just your word that it's not warm enough. At the end of the day though it may not be comfortable living with a hostile landlord unfortunatly. You could also contact the local city councilperson to perhaps mediate the situation. Document all correspondences, emails etc. you'll need these.
Massachusetts is a very pro-tenant state. Typically also whoever draws up the contract if there's a dispute it's usually found to be in favor of the one who did not draw it up (typically tenant). Even with rental agreements, leases ect. it cannot hurt to have a qualified attorney review the contract with you & explain any questions you might have. We're not attorneys and cannot give legal advice.