I booked main cabin, which was supposed to be changeable, but not refundable. I got advice on this board about reading Delta's "contract of carriage" which is basically the fine print, and differs for every airline. In it, Delta states that if your flight is changed more than 2 hours from your original booking, you can request a refund, regardless of ticket type.
When I contacted Delta, they told me they wouldn't refund me, as soon as I mentioned their contract of carriage, they immediately transferred me to a supervisor and she processed the refund.