Why would they? Award ticket fingerpointing is a worldwide issue that virtually all airlines are awful at. Ticket stock airline A, flight with airline B. No one wants to take responsibility, and courts are unlikely to.figure out who's at fault - Greek or not.

As others have suggested, try to get ET to release availability for you, or commit to, them get A3 to book it. The reverse won't work, from experience, as A3 generally won't bother contacting airlines direct to resolve award issues. Also set alerts, ET release good availability all the time and it's possible these will become available again. Finally, check the individual legs into and out of ADD to see if either has availability, and therefore if there may be other routings that work.