New accounts that have much winning on their first trial usually have suspicions from the casino and they may even lock your account so I think you are lucky to have that but don't try it next time because you might not be lucky next to win talk more of been able to withdraw the money, some casino will flagged your account of cheating and they may ask you for more verification process which will even take more time than the regular time frame of verification.

I'm not sure about the casino controlling winnings but I'm sure you are not the only player in that casino, If there is such thing of controlling of winning, I'm very sure that a lot of complaints would have come from there as people will see them as scammer. Every casino has an house hedge which differs from each other, I'm thinking that that's how the house hedge make their players to win and lose and it happen you were unlucky to loss your money.