How to deactivate F&O account permanently?

I know kill-switch feature. But it’s temporary. One can reactivate after 12 hours and blow up entire account.

Just curious, Why do you want to de activate it permanently ?

*deactivate, for obvious reasons

You can deactivate (not close) your account by submitting an account deactivation form, after using this method you can only reactivate the account after submitting an account reactivation letter. You can learn more on this here.