I listened, heard them out and empathized, I then explained calmly and simply what steps I would take to attempt to resolve the issue, then act on them. Usually people don't need you to fix their problem right there, they just need someone to be confident with their answers. "We will try X Y and Z and if the issue is still not resolved we will escalate".

have a clear overview of your workload. List all the projects, tasks, and deliverables you have for each client, along with their due dates, urgency, and importance. I would use a tool like a spreadsheet, a calendar, or a project management app to organize and track my work.

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