It happened to me once, I received 2 times my btc withdrawal in my wallet. 500$ x2 . I was a bit anxious so I told the casino; customer support told me there was nothing unusual on their side.
I asked are you sure, because I definatly received 2 withdrawals in my private wallet? They said yes..
Nothing since then, I haven't tried another withdrawal tho.
I know some casinos do have sections in their T&S specifying they will ask their money back in case of an error But quite frankly, I don't know what's their legal rights in that matter.