I have used the form online before and within 5 business days, I've received email confirmation of the cancellation and full refund.

Once the web form wasn't working. Called my DL Medallion Desk, who immediately cancelled the ticket and filled out a "universal refund form" on their end. I did not receive further correspondence, but the PNR was no longer valid as soon as I got off the phone, and the refund came shortly thereafter.