Keeping calm is key; reactions such as anxiousness or anger--while natural--will make things worse.  If the customer views you as calm and professional, the customer will tend to "mirror" your reaction.   Try focusing on your breathing, by taking deep, calm breaths. Do not be obvious about breathing heavily, however--it may come across as creepy or sighing. Let the angry client talk through their problems and explain all the reasons they’re unhappy. Do not interrupt. If you have a question, wait until the person is finished to ask it.  Be patient. This may take time on the customer's part. Do not argue, contradict, or otherwise engage in a fight, even if the customer is patently wrong. If the customer feels heard, it is often the most important part of the interaction. Customers will often eventually become much more agreeable just because they are listened to, sometimes even if the issue cannot be handled. An angry customer probably won't be careful about the specific language they use. When they say, "You messed this up," they usually mean the company messed up. Remember that this isn't about you, and taking it personally will stress you out unnecessarily. The customer cannot see you, so some verbal feedback helps reassure that the line has not gone dead, and you are listening. As they talk, make indications that you are listening, such as "Uh huh,” “Okay,” and “Oh, wow.” This will assure them that you are paying attention and make them feel like you want to hear the whole story. Your instinct may be to raise your voice in response to being yelled at, but this will only make matters worse. It will escalate the conversation to an argument, and the customer won't trust you to help them. Keep your voice level throughout the call, never speaking above a normal conversational tone.

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Write a summary of the previous text in Indonesian:
Jangan bereaksi impulsif. Biarkan klien mengungkapkan perasaannya. Jangan tersinggung. Berikan tanggapan singkat secara verbal. Kendalikan nada suara.