Depression is truly a soul killer. And it might be a slippery slope towards suicide if we don't get a handle on it, both personally and as a society.
When you ignore your kid's messages and voicemails you are giving them a very powerful message about their priority in your life. There is nothing you can say afterward, the exasperation has already taken place. This is never a happy response, "I don't know, I can't reach her and she's not responding."