I'm also sorry this happened to you after so much hard work on your part.
I'd definitely file another complaint/request with customer support, and file as many as it takes to get a satisfactory resolution (aka: your dragon). Keep pushing them. The whole "you have to ask before the event ends" response is completely unacceptable, it makes zero sense, and is them trying to give you the run-around, hoping you'll just go away and they won't have to deal with or admit their mistake.
I know for a fact (from past experience with a glitch during the Tales with Glasswing) they can send a prize dragon AFTER an event has finished to players who have suffered a glitch through no fault of their own. Keep pushing. What they did is NOT right or ethical, and they MUST make it right for you (and anyone else who lost their prize due to the event finishing prior than the posted time). If they won't, file a complaint with the Better Business Bureau and Apple (or GooglePlay if you are on Android). I know Apple, in particlar, takes this type of shenanigans very seriously.
An ethical company would send a dragon to every player who particpated in the event since the event expired before the clearly stated end time.