Numbers like that come from a variety of senders. What message are they leaving? Is it the same odd number each time? What else can you tell about it. I've seen odd numbers from Verizon, Facebook, Twitter and others. But what's their message?
That sounds strange. Have you checked your call stats on your My Verizon account? Have you called and spoke with Verizon Customer service? They're very nice and helpful. They do read a lot from a script, but if they don't know, they put you through to a tech.