I rec'd an email stating my 9pm flight ATL - LHR was changed to a later, midnight, flight. New seat assignment attached. No explanation.

The new flight is hours later, and my seat was (semi) downgraded, to a middle section aisle. No other desirable seats on the new flight.

However, the original flight (9pm) is still scheduled, still selling and the section I was originally seated is completely full.

2 agents at Platinum line were clueless and unable to resolve.

What do you think is going on? How can I pursue this? (I've opened a CS file on DL.com).