I got a lot of that from more experienced agents when I first started in the business.  I've got 30 prior years of experience so I'm fairly comfortable dealing with those types of situations.  If I felt like a particular agent was not responding, I would call, leave a clear, concise voice mail, being as polite and professional as I could be, and I would follow up in writing with an email and blind copy myself.  IF I did not get a response after a day or two, depending on how critical the issue was, I would contact the brokerage and ask to speak with the managing broker, and I would inquire if the particular agent might be on vacation or out sick.  I would explain why I was calling and that I had made several attempts to reach the agent, and was concerned about not hearing back.

That approach usually yields results.   Most agents try to avoid answering those types of questions from their broker.