You are right in what you are saying: when users of a casino's platform are not given what they deserve, it can be considered scamming their client users.
But if it's just an accusation and no strong evidence can be shown, it turns out that they're just defaming the casino platform, right? Because it will turn out that in the end, if there is no evidence, it will just be a rumor or a false allegation in a casino. Though I'm not defending Wintomato,.
Wintomato has an active issue against @efialtis which is a reputable member here that involves on casino industry. They have almost same issue with OP which wintomato doesn’t honor their referral commission percentage agreement. Reading this thread remind me about the issue and makes me believe that OP has the right to make an accusation against this casino.
You can check the trust history of wintomato for the negative feedback sent to them.
https://bitcointalk.org/index.php?action=trust;u=3346646