I let them yell. Interrupting or yelling back does no good. “Kill ’em with kindness” rings true. Obviously, if someone is yelling, they’re either trying to make a point or are out of control. Either way, stay silent and let them finish their childish rant.
Then take control of the conversation back and resolve the issue.
Hi, In this case you have to first listen to the hole scenario what happen to the customer. Let him to give up the grouch (sometimes it will take 10-15 min to listen. No matter, just listen). The ask the apologize and then explain it.
Just let them talk, the client is angry and will not listen to you until done on his/her explanations. When she/he stop that is the time you need to apologize and do not promise anything. Just let them know that you will check and follow up their inquiries.