I think the double payment should be paid back. In real world its probably true that, if you send someone money through wire and you accidentally changed a number that you dont get your money back but its a different thing for businesses. For example the cases where a bank send one of their customers some million euro and he has to pay it back of course because its not his.
The double payment mostly isnt worth the amount of assets one owned but you can be sure that nef wont run the assetinfo until this money is back. So you can try and blackmail nef with not giving back this money... but why should he care about? Its not his money and he showed that he wants to pay back most of it. So blackmailing him will only lead to the point where he can point with the finger at you guys and say "Look... these are the bad guys" and nothing will move. You know its true. He hasnt shown any responsibility for the damage he caused and feels he is doing everything right. Wants the last months ceo payment and so on even though his shareholders probably suffered higher loss than this because of his actions. I mean would you stop a business this way that afterwards everyone is angry at you? I mean when i would do it i would expect that it will cost me something. And when its only to not leave them all angry.
You try to blackmail him... with money that is not nefarios but belongs to other normal users. He wont care. Why should he? And why should he follow the blackmailing?
You guys deliver him a perfect excuse to not going further.
Perfect business trick.
Now he sent double payments & ordered to return the bitcoins
Or this ^ (deleted some of your lines) is the business trick because nef can be sure that at least some dont pay back. So he could create a perfect excuse why he cant process the sharesinfo.