In every organization and every business, we have to deal with angry customers.
Some of them are so angry the situation can be hard to diffuse.
When a family saves money for years to visit Disney and something goes wrong, they can get very angry. When a situation got to me, I did what ever I could to solve their problem.
Remember, they are not mad at your personally. They have 10 other problems you don't even know about. Don't take it personally.
The customer is not always right, they are often wrong. But they are always the customer. And you if you want them to be a repeat customer you do what you can to turn the situation around.
Don't get defensive. Use empathy and try to solve the problem.
Do your best and then forgive yourself. That is all you can do.