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No, you are missing the key point here. It was a deposit address of another user. Therefore, the funds have been credited to the account of that user. Most probably, the user has already played with the funds and made a withdrawal or lost it. Stake isn't liable in that case. The situation is like sending funds to a wrong address.
But even this was a "deposit address", now the funds have been credited to the new player?

? I am asking because I have serious doubts this has been really done... however both sites have been really ignorant on how they manage the whole issues.
it seems they have never seen previous a similar transaction and they managed like rotten eggs. Funds are in their wallet. It is not impossible to retrieve the funds...
At this point, I think that a good lawyer (or even a gambling association / local authority ) could be the proper solution here...