Respond to an angry client email

You are an Account Manager at a marketing agency. You just received this email from David Park, the founder of a startup client you have been working with for 3 months ($4,500/month retainer):

"I am extremely disappointed with last month's work. We paid $4,500 and got three blog posts and a social media calendar that looks like a template. My competitor is running circles around us and I feel like your team is not taking our account seriously.

I want a full explanation of what we delivered and why it justifies the invoice. If I do not hear back by tomorrow I am pausing the retainer."

Write your response to David.