Why send a letter to the are souls who are going to tell your family and friends to shun you? Why do you owe them a letter?
If you feel compelled to write a letter, consider mass mailing it to all of the people that they are going to warn not to talk to you from now on, and don't send a copy to any of the hierachy of this pathetic little cult so that they don't get the opportunity to warn the proles not to read it.
It's like talking to the JW at your door. Never talk to the one that is obviously taking the lead. Address your question to the weakest one and put the psychological pressure on them to be the one to answer you.