So I’m flying from MCO-DTW-SDF tomorrow morning on a paid FC ticket. I check in this morning and all is well but I get a notification from my Apple Wallet saying seat changed to 15A from 4A. I go into my reservation and see that there has been an equipment swap from a 753 to a 75D and there are 0 FC seats left. I immediately started to question why I was bumped because the flight was basically empty in FC before the DM window so I had a feeling that the majority of pax were free Medallion UGs. I then called DL and the first agent I spoke to was useless and refused to take this up to a supervisor to investigate and only offered to give me a refund on the difference between FC and C+. I HUCA’d and the next agent did elevate it to a supervisor and as I predicted told me that there was a glitch and I shouldn’t have been downgraded and told me that they were working on it and that I will have a FC seat by the time I get to the gate. I’m really wondering weather I should call back again because I’m still in 15A and I don’t know why her supervisor couldn’t kick someone else out right there and put me in FC. What would you guys do?

Update:
Just got off the phone with two different DL agents. The first one was basically useless and told me that everyone else in FC had paid more for their ticket than I did (I know this is false because I know someone on an award ticket in FC who is still in FC) and offered me a $100 travel voucher. I called back and the second agent told me the same thing the lady I spoke to earlier said that there was a “glitch” and I should have a FC seat and it has been notated in my reservation and I will receive a FC seat at the gate because the flight is already under airport control.

Try to get to the gate early if at all possible, ideally to talk to the GA as soon as he/she arrives and signs onto the terminal. You don't want to risk the flight having an empty FC seat due to SDC or whatever and having the GA upgrade someone else without looking at the notes on your record. Some GAs are extremely reluctant to ever downgrade someone who has been upgraded at the gate, even if it's an obvious mistake. Also, be prepared to ask for a redcoat if there's a problem.

ADDED: I'd also try to talk to someone before the gate, either at the check in line or in the SC if there is one at your airport.

It also wouldn't hurt to watch the seat maps between T-24 and departure. Be prepared to call and pounce on a seat if one becomes available rather than risk it being given to someone else before the gate, although this is probably unlikely if the flight is under airport/gate control.

What is and what should be could be two different things.

Yes I am on DL2821. The problem is that I am traveling with a companion who is on a FC award ticket and there is only 1 other empty FC seat on the other morning MCO-DTW flight. I would prefer to go through DTW vs ATL to maximize MQMs.