I am a PM. I called around 3pm ET and requested a call back. At 7pm when I still had not been contacted, I called again an just waited on hold...I was connected to an agent after about ~10 minutes. I was calling to see about getting a refund or delta credit for two FCM upgrades I had purchased for a RT departing on Sunday (the original flight and the FCMs were purchased ~two weeks ago). I know these are non-refundable, however I had seen a few posts mentioning some folks had success. My plan was to contact delta first for the FCM refund/credit, and then I would contact Amex GBT (my corporate TA) to cancel the original RT flight and get a credit, as the fare was non-refundable.
My entire call did not last more than two minutes. I politely asked for "if my paid upgrades could be refunded to my cc or to a delta credit, as my company has asked us to be thoughtful about our travel, and since this was not mission critical, I was going to call my corporate Amex travel to cancel and get a credit for the RT when she was done." She responded and said "you should get an email in a few minutes with the refund details, and to call back in 7-10 days if I did not see the refund." I thanked her, ended the call, and waited for the email.
About 10 minutes later the email came in. To my surprise, she refunded both the FCM and the original ticket, each to their respective original forms of payment! Makes my life easier as it's one less thing to expense, and one less ticket credit to keep track of to use for a future trip.
tldr: When you call, don't ask for call back, stay on line. FCM refunded, as was original ticket (without asking) to original forms of payment.