I am a young writer who actually isn't that naive or arrogant enough to think that my writing deserves publishing (but I can dream right?), however, I at least think everyone is entitled to a response. My young adult novel has gotten to the full stage with five - count them - five different agents. After at least six months for each, the agents have not replied to my check-up e-mails or phone call. One agent said they were still reviewing, but that was two months ago (after the six months). Do I have the right to be frustrated, or should I be happy that someone even might be considering my work? Or maybe the silence of the five is a consensus of suckage toward my writing? What kind of message does it send when you take the time to write a novel, edit it, send it out, get requested, and then hear nothing?
You mean all five agents not only have kept you on hold for 6 months, but also don't answer phone calls or emails? Wow. They're jerks. I would be frustrated. Ignore any exclusives you may have given and start querying other people.
Publishing is frustrating - to writers, to agents, to editors, to the guy who has to design the cover that nobody ends up being happy with - we're all very frustrated. All the time. There's a high burn-out rate in this industry. On the other hand, we occasionally get to make dreams come true, which is pretty cool.
Your manuscript is obviously of some potential for so many agents to have considered it; start querying again and hang in there.