I think your letter is well written....
I would advise you TO NOT SEND ANYTHING TO THEM. By sending this letter your are giving them some degree of validation; playing by their rules.
By just turning your back to them and going on with the rest of your life you are sending the message to them that you are taking control of YOUR LIFE and do not consider them important enough to acknowledge their position.
Whatever you decide; good luck to you.
Frank