Sorry buddy, as much as started disliking Blizzard thanks due the Nost shutdown, I'll have to side with them on this one.
As far as I understand, you have purchased a bundle; the entire game, everything since classic and every expansion up to WoD, plus access to Legion. So you have already played through a majority of what you purchased - of course you're not entitled to a refund there anymore. That'd be a bit like ordering a meal, eating most of it, and then trying to send it back after you've finished most of it already. Or ordering a new computer, and after a year deciding to send back the DVD drive only because you haven't used it yet.
If a company is super really extremely above-average friendly, they might accept it voluntarily, but there's absolutely no obligation too, and most businesses in practice would most certainly act the same way in such a situation.
I very much welcome everyone trying to cancel their preoders after the Nost shutdown, financial consequences are the only thing they might understand in the end. But in that particular combination, their reaction is pretty much business standard.