but I am afraid to send a letter to my old KH. What should I write to make sure they don't just DF me?
Any letter sent to a Bethel Office would be simply directed back to the congregation for action . A letter clearly stating that you are longer to be called a Witness would provoke the generic announcement that "White Waves is no longer one of Jehovah's Witnesses"
The Bro's would not know whether you had been d/f'd for something really horrible or whether you had simply d/a'd yourself. To them it would not really matter. You were to be treated as a d/f'd person anyway. Reminds me of Orwell's 1984
"Syme had vanished. A morning came and he was missing from work. A few thoughtless people commented on his absence. On the next day nobody mentioned him . On the third day Winston went to the vestibule of the Records Department to look at the notice board. One of the notices carried a printed list of the members of the Chess Committee of whom Syme had been one.It looked almost exactly as it had looked before - nothing had been crossed out - but it was one name shorter. It was enough. Syme had ceased to exist ; he had never existed.