Call whoever issued your ticket and ask to be rerouted. As you rightly identified, your Cuba trip has made you ineligible for ESTA, obtaining a visa is probably not feasible in the time you have, and the US will not allow you to transit without either of those.

Good luck, hope it works out for you!

Edit: Just re-reading your post, it sounds like you already have an ESTA. I'm not sure if this changes something compared to applying for a new one. I'm sure somebody will be along shortly who knows...