To handle angry customers, use the six step method: Listen, empathise, question, answer, confirm, close.
Listen without interruption. Start to take a few written notes.
Empathise with their emotions. Let them know you understand how they FEEL.
Ask questions, so that you understand the facts, apart from their feelings.
Formulate a practical plan, that will best solve the customers problem.
Confirm their understanding of the plan and take steps to implement it.
Close the call. Finish your written notes and move on to the next caller.