I think I'm getting to understand your case fully right now, and for me I think if only you can proof that your complaint was made before the game was played and you lost it, then you truly deserve your betting refund (i.e $1000), But if the complaint was made after the game got played and you lost it, then... (I reserved my comment). And I think it's at this point, I let the casino representative do this job regarding this case, as I'm really interested in this case and will love to see how it ends. However, I'm wishing you good luck.
Whether the bet was lost or not. IMO, it's still not ethical to accept a bet that has an old odd when odds have already changed because it can later on cause issues. Let's put it the other way round. What if the odd had dropped from 1.5 to 1.2, OP stakes 1,000 and potential win is 1,500 according to the old odd instead of 1,200.
Do you think the sportsbook would stomach that? Personally, I don't think so. They would consider the bet void due to a system error and probably just refund the initial stake.