Use of 'Until' and 'Not' in a Sentence

Is the use of "not" in this sentence correct or not?

Don't communicate until the phone line is not fully secured.

Kindly advise.

Well, you have a double negation in your sentence, so you're basically saying "wait for the phone line to be unsecure/unsafe, and then start communicating". From a grammatical standpoint, that sentence is 100% correct; there's nothing wrong with it. But, that's probably not what you meant to say (who would want to communicate over a dangerous, unsecure phone connection?). What you probably meant was, "wait for the phone line to be secure, and then start communicating". In that case, you would write:

Don't communicate until the phone line is fully secured.

EDIT: changed "insecure" to "unsecure"