You need to send a certified letter to the Boston Police and to the municipal court handling your case advising both of them of your change in address.  When the green card or delivery verification is returned, this will give you evidence that you did attempt to notify everyone of your change in address.  From there, check in with the court regularly until you finalize your fine.  If this still doesn't work, then considering hiring an attorney to help you finish wrapping up the details of your case.