Most importantly is for you to STAY CALM! Let the customer, individual, etc. know you're listening to them and can appreciate why they are upset. They want to be validated. This will also aid in calming them down more quickly as well. From there, gather as much information in a brief period as possible of the situation, but NEVER give definitive answers until you are sure of the outcome. Either you yourself or once you speak with management, things are easier to decide what actions should be taken moving forward.