My next course of action is to call the agent, send them a text message, or email them, sometimes doing all three. Who knows, maybe the file was too large to get through email. Amazingly, these agents never return my calls. Is it embarrassment? Probably, but I chalk it up to pure old unprofessional behavior.
Like most people, I hate it when my time is wasted. So now, I don't contact my clients until the offer is in my hand. What's the point of disappointing them as well and wasting their time? So the lesson of this story it, don't tell me about an offer unless you actually have one.