You are right sir, casino companies are legitimate bodies that are been operating legally, so refusing to pay me my win after all evident is been proven is a breach of contract and it's a punishable offense. I will be left with no option than to sue them to court and hoping to see a better result from it.
Because it is very unfair and seem unprofessional of them to practice that kind of a childish attitude, what are you telling your customers, that you are not reliable, not truthful or not capable, is really crazy because such attitude can scare away most of their users.
The casino's refusal to pay after a win might be because of several reasons. And this could be the fault of the casino or the winner. Casinos that lack a reputation could do that just to avoid paying. They might come up with several excuses, which might include violating the terms of service. In such an occasion, the gambler should report to the relevant authorities.
The player could be at fault if he fails to bring a valid ID or it is discovered that he violated the ToS. In my case, I would report to the police and forward a complaint to the gaming regulatory body of my country.