You need training. In the meantime read stuff. Like this...
http://customerservicezone.com/faq/indexangrycustomers.htm
http://m.wikihow.com/Deal-With-Rude-Customers
The reason OP can't fix it is because she does not make the rules. She can't change the rules.
You will learn "buzz phrases" like
I completely understand
I am going to work with you to resolve yor issue
That makes me frustrated too, I will let my boss know
Angry people are illogical.
Once you master this you WILL be marketable.