Something like this could have happened.... I posted here, that I won £800 there after doing the same as you, I deposited £40 .. anyways .. I withdrew £500, or thought i had, checked the account 2 days later for a game, and the account said £800 .. So I withdrew the £500 again, and just today it showed up in my bank ...
So if I were you I'd withdraw again but keep checking daily that they haven't put it back in your online account
Oh it's the 26th tomorrow ..so get going quick .. I wrote here on another thread about this , think well pass on that league thing if it starts in the spring .. glk mate