That sounds like a frustrating situation. It's understandable to feel concerned if a casino asks for Know Your Customer (KYC) verification after winning an amount above the usual threshold.
It's not far from the truth that such things happen. So, before you enter a casino, check to see whether there are any negative reviews about that site. If you've ever made an account, make sure that if you withdraw, there's nothing wrong with your account so that the transaction goes smoothly. Aside from that, there are people who are just suspecting you, that's why you have to supply the documents for them to validate, just provide what they ask and don't protest if you see them trying to swindle you so that your situation will be resolved as soon as possible.