When in customer service if a customer yells what do you do?

Calm yourself, and listen to the customer. The problem has nothing to do with you personally. Listen for the content: what is the customer upset about? What does he/she want out of this situation and think about how you can help him/her? Underneath the anger, what's the customer feeling: frustration, disappointment, etc.

Reflect the customer's feeling and situation and to him her, and state what you're going to do about it: "I can understand why you'd be frustrated about all the phone calls you've had to make about this issue. Let me do a little research and find out what we can do about this situation. Will you be at this number in 20 minutes?"

That is, if you can't solve the problem then & there, provide a time frame for resolution to the client. It's the unknown that frustrates customers, and the feeling that they're being given the runaround.

Vasily

It makes a lot of sense what you just answered. Thanks