Is this a short sale? if so, the hold up can be with the sellers bank.
As for your realtor not answering the phone, that is just not acceptable. You should contact his/her broker.
Fact is, if this is a short sale your agent has very little influence in getting things moving. He/.she is at the mercy of the bank as is the seller's agent. That being said you should be kept up to date on the status of things.
Agents do not like to deliver bad news, and having to tell you they have no new news to report to them may seem like delivering bad news.
Try to hang in there, stay focused and strong. You may not hear anything for a while, and THEN all at once things can start to take off very fast.
I wish you the very best.
Kawain Payne, Realtor