The problem is here that I can just see my betting history. There is no such Casino's History. And how can I prove this? I asked 1xbet for details on money cashed in slot game, but they didn't respond.
It took me just to google this website to find out that it has a terrible reputation. One of the first reputation-related links leads to the following website where 1xbet has terrible reviews:
https://www.trustpilot.com/review/1xbet.com. Most people say that there are problems with withdrawal, and there are many scam accusations. Moreover, when I tried to open the website, it said in Russian that the access is closed, and there's only a non-free option... Sorry, but all you can do is open a scam accusation on Bitcointalk to warn others, but I would not expect to get the money back.