I worked in a call centre last summer and my job was to deal with customers whose accounts were overdue. While most of the customers understood why they were receiving the call, one particular customer reacted in a very aggressive and abusive manner. I tried to explain to him that I was only doing my job but he didn't hear me as he was shouting so loudly. Finally I had no choice but to put the phone down as nobody should have to put up with this kind of abuse.
It may not have been your ideal job but, in terms of handling a difficult customer, this is not a good example. Your answer shows that when things got tough that you didn't cope. You had other options including perhaps putting the customer through to your supervisor or allowing the customer to vent their anger first and then ending the call in a professional manner.