Originally Posted by
Hemera
1. According to Regulation (EC) No 261/2004, I should have received a refund of $2,089.98 * 75% = ~$1,500, i.e., $300 more than Condor had paid me. Is there a straightforward way to dispute the amount of the refund?
You are entitled to a refund of 75% of the "price of the ticket." Per ECJ case C‑255/15, the "price of the ticket" apparently doesn't include mandatory taxes and fees. There is potentially some room to dispute if some taxes and fees are mandatory or not. More info
here.
Originally Posted by
Hemera
5. Most importantly, is there a way to get back the remaining $889.98? If yes, what is the best way to go about it?
You can maybe get some help from article 5 on cancellations in the EU regulation, if you could argue that your original business class flight was cancelled and that you were rebooked. If the schedule and flight number didn't change, then it could maybe be disputed if this was a cancellation or not. If it does count as a cancellation, you should have been offered a choice between three things under article 8: a full refund of the "price of ticket" (the airline can maybe keep the taxes and fees) or "re-routing, under comparable transport conditions, to their final destination at the earliest opportunity" or re-routing at a later point. I don't think that economy class is "under comparable transport conditions", so you might be able to demand that you still travel in business class.