It happened to me last week when I deposited 0.06 BTC on a casino just for 100% deposit bonus promo, I played on slots there but just in a minutes lost that amount of 0.12 BTC same without winning anything there, slots always very bad to play there because players very low chance to make profit.
Well thats bad.and sorry about your loss. Its gamble and it always happen. To win or to lose, thats is gamble. You are hurt because the amount you have lose is high and you have not win anything.
Dont gamble if you dont want lose your money or bitcoins coz this is gambling is for. Dont expect you'll win always.