It is from the American Conservatory Theater.

Yes, it's a real person calling from the box office of American Conservatory Theater in San Francisco. They have my number (I often go there) and they wanted to know if I was interested in a particular show (to which I already had my ticket, but they didn't realize it).

purchased a Groupon for ACT for 6 series of tickets for two in 2009 and ACT has been calling me ever since to purchase another season which I never will because the seats suck (not cost-effective in the long run, too uncomfortable in balcony).

I hate when they don't leave a message. Thank you 800notes.com for helping me solve this mystery!