I dealt with a Delta refund just last week and it all worked out without too much trouble. There were two different Delta numbers that I called, 1-800-323-2323 and 1-800-847-0578, the latter of which is the refund line that's staffed during regular business hours EST (I believe until 8PM).

You can also submit a refund request online at https://www.delta.com/contactus/iropForm

I was admittedly late in contacting Delta... our flight was scheduled for Fri 5/15 and I first called Weds 5/13 after normal business hours. Since I wasn't sure if I would be able to get in touch with a Delta agent prior to the flight I proceeded to submit an online refund request.

I called back on Thursday evening 5/14 around 6PM, and with speakerphone turned on I went about chores at home while waiting on hold. The agent picked up around 7:30PM. I made the agent aware of my issue... our nonstop flight from JFK to STT was changed to a connection in ATL, and the first flight from JFK to ATL was scheduled to land an hour AFTER the ATL to STT flight was scheduled to depart. I also gave the agent the case # for my online refund application. The agent quickly acknowledged that I was eligible for a refund, not only because Delta had rescheduled me to an impossible connection, but also because the change from nonstop qualified as a "service downgrade".

The agent placed me on hold while she processed the refund. She returned 5 minutes later and told me that it would take approximately 30 days to process the refund, and may take up to two billing cycles for the refund to appear on my statement.

I received the refund earlier this week, less than 5 business days later. Hopefully you have the same luck.