Ever how hard this is to do, I find the best thing in these situations is to stop trying to talk to the person. More often than not, given time, they will call back and talk to you again, and if she doesn't, well, you'll get over her eventually. If she doesn't care about you enough to at least call and explain what's up, then she doesn't deserve you anyway.

Sorry that you're having a rough time, I hope this helps at least a little.