In this regard you missed an opportunity though. Since you say that you win by betting with small amounts. I think you should have played with smaller amounts. However, no such complaint was found on any reputable site. When you bet more, your luck doesn't favor you. Or it could be that the site is cheating you. But for this you must collect proper evidence. Otherwise you cannot take any action against them. If your doubt is strong and you can't gather any evidence, you may be better off choosing another good site.