Keep calling and either breathe in phone, like a sigh, then quickly hang up after voicemail beeps for them or a very long voicemail of nothing.

I tried calling back twice. Both times was immediately message: "Is Unavailable. Good-bye." Then automatically hang up.

Called again from a different phone and a different message: "Please stay on the line. Your call is very important to us." Music plays. "Good-bye." Automatically hang up.