I'm not sure what your situation was, but yesterday, I called LL with an account problem (I'd erroneously cancelled my account, forgotten I'd cancelled it, and couldn't figure out for the life of me why I was locked out. :matte-motes-stress:). The woman who helped me wasn't upbeat by any stretch of the imagination, but she was quite pleasant and helpful.
As a former customer service representative, I can tell you that they often mirror their callers. If you call crying and sharp-tongued, many will be abrupt with you. They likely receive an onslaught of abuse all day long, how would you feel in their place? Everyone has limits. Stay calm, be polite and pleasant, and your CSR will probably return the favor.
That said, I know the it's the CSR's job to be decent and professional or seek out different employment, but we all know the real world doesn't work that way.
Now that I'm a customer rather than a CSR, I try to remember what it was like to have people shriek at me, and regardless of how angry I am, I try to play it cool. After all, it's not that particular person's fault I'm having issues. Shrieking at him/her is no different than walking up to a complete stranger in the grocery store and yelling at him/her because the store is out of your favorite brand of cereal.