Sorry I came to this thread late, but I just now found it.

I can't say for certain what you should do without knowing more about what was said in that original conversation. You wrote:

the person who I spoke with said, "We'd love to have you play..."

It's that "..." that bothers me. Three dots is an ellipsis, and an ellipsis normally means you're leaving something out. What are you leaving out? What else did they say?

If "we'd love you have you play" is ALL they said, then I'd say you don't have a contract.

If, on the other hand, they told you a specific time and place they wanted you to play, and (especially important) if they told you a specific dollar amount that you would be paid (or, equivalently, a specific formula by which an amount would be calculated), and you told them you agreed to it, then you DO have a contract.

Sure, it's an oral contract, but an oral contract IS a contract nonetheless.

If it bothers you that they seem a bit disorganized, then I'd say cut them some slack. Festivals like this are often organized (to use the term loosely) by volunteers. Sometimes the volunteers are inexperienced. Sometimes they don't communicate very well with one another. Maybe the person who contacted you expects someone else to follow through and contact you again. Maybe they lost your phone number. Who knows?

If they are acting like amateurs, then it behooves YOU to act like the professional, and guide them through the process. Call them and tell them, politely, what you need in the way of confirmation and/or instructions and/or payment.   

And I agree completely with everything Artful Codger says about answering machines.