1. Three different issues: A) Refund; B) Compensation; C) Customer Service.

2. No matter what the circumstances, you are due a refund of the fare difference. Here that is the miles and you have already been told that you will receive those.

3. There is no compensation under the COC.

4. UA generally provides a customer service gesture in the form of an certificate for $250-500 depending on distance.

But, in order to be eligible, you must have met the deadlines for check-in and presence at the gate. In your case it is a little bit confusing as to whether you were checked in or not. If not checked in, the F seat is simply reassigned if needed and there is no CS gesture involved, just as if you had missed the check-in deadline for a Y seat and it had been reassigned.