I am always very courteous, even when student loans fucked up and didn't pay my tuition. It took 3 months to get that sorted out. I got a letter of appology, and they paid the late fees (over 500 bucks) for me. I was patient and never raised my voice.
I started to take the person's name that I was talking to, as well as take notes.
"Student Loans, Can I help you?"
"This is Ben calling. Who am I speaking to, please?"
"Uh... my name is Carol. How can I help you?"
"Well, Carol, when I called yesterday, Jeremy said that he was going to contact the University and correct the problem. Can you look into my file and either confirm or deny that occurred?"
What have I just done? I just told poor Carol that I know who she is, and she will be held accountable for her actions. She is no longer a nameless/faceless drone at the call centre. I will check up on her to make sure she is telling the truth.
I got results. And fast.
I have since adopted that strategy for all of my phone contacts. I believe that it works well for me.