I have made some findings about this before if I remember correctly. There are people that have sued gambling sites before but the result has always been the gambling site winning the lawsuit. So just know that if anyone sue any reputed gambling site, the gambling site may win the case.
The case of those two brothers against bet9ja is still in court they later sued the casino over denials to pay off their winnings, I think that was the only court case against a casino that I have heard or seen all the entire time, and even at that, those guys have not been able to get justice from the legal fight the betting site have not paid them they winnings up till now.
One of the reasons why most people don't adopt that approach of legal means to pursue their case with betting sites is because at some point it is hard to battle with them since some of them are not registered in the country.