Well, I believe that in order to handle any escalation/calm down an angry client/customer we first need to be a good listener, that solves mostly the 70% of the problem as you allow the person to vent out everything they have in mind. we need to be active in IQ and EQ given the circumstances and take action and present solutions, accordingly. As we should always adhere to the guidelines/SOP of organisation, however when we are dealing with a Cx really upset we need to make them understand that we are one among the, just another user/cx in this world only and would not feel any different+ follow the path of Apology> assure >educate them in order to solve the issue and always add personal touch in the end to ensure the client/customer that nothing will go unnoticed/un-actioned.