The first step is to apologize. You want to make sure that the customer feels that you are sorry, that they are dealing with this, and that you are going to reassure them that you are going to tackle the issue together. You want to be able to ask non yes or no questions, but open-ended questions of what exactly is going on? Okay, how would you want this resolved? And figuring out from there how to fit the solutions available to what they need. And if they are being difficult, the biggest thing is to remember not to take it personally. They are frustrated at the problem, not at you.