Ask them to do a long sell (they know what it means). If they play dumb, ask them to contact AF directly to check inventory. If it's showing up at AF.us as available, and you can see O class available on EF, it should show up on DL.com.
Just make sure that it is really business class showing for 50k one way on AF.us. Click all the way through to the booking page to make sure it's really there.