You haven't disclosed the destination, so we have no way of knowing if there is once-daily service or if you could fly from another US connecting point. Presumably it's once-daily, in which case there aren't any alternative flights to offer you. However, this offer is really pathetic. As a point of comparison, I got $300 to move from F to C+ as a voluntary downgrade. My flight was SLC-ASE, so about 30 minutes in the air in a CRJ. Your downgrade was involuntary, and if you lost a flat-bed seat on an overnight flight, the compensation should be much, much higher. I would keep fighting and escalate as needed. It may be a SkyMiles award, but it's still a confirmed J seat and $200 is a joke.
If there are any partner airlines that fly to your destination, you could push for that even if there is no award availability. If not, you might want to explore if you can fly Delta to another South American city in J and then push them to pay for a non-partner ticket to get you to your final destination.
Last edited by Billy Mumphrey; Nov 8, 2018 at 2:37 pm