You'll have better luck serving angry customers if you make them feel like you're on their side. This is called the Partner Technique.
Here are some examples of using partner behaviors:
Shift your body language so you're both facing the problem together
Listen carefully to customers so they feel heard
Use collaborative words like "We" and "Let's"
It's hard to be upset at someone who wants to help us. Most customers naturally calm down when they realize you are listening to their issue and trying to be helpful.
One final note: Being on the customer's side doesn't necessarily mean you aren't on your company's side. It just means that you are making an effort to understand your customer and help them succeed.