STADD,
Responding in anger is always a bad idea. Always.
You're right. They are being cruel and unloving. They are in a cult.
Write a letter when you're pissed if you must, but put it in a desk drawer and don't mail it.
Then, when you're calm, try a more reasoned and compassionate approach. After all, they're in a cult and you're not. So don't respond like you still are too.
They are immature and throwing a temper tantrum. Don't respond in kind.
Seek to reach their hearts and minds if at all possible and lay out clear boundaries, but please take the moral high road. Please.
Oubliette