Double spending is possible with Bitcoin transactions. I am guessing this casino accepts 0-confirmation transactions, am I right? In other words, they add the money to your balance before the transaction occurs on-chain and allow you to play with it. But you can't make a withdrawal before the transactions confirms.

I have a few questions.   

Was this the address you often used to deposit from and to the casino? It seems to belong to an exchange.
https://mempool.space/address/bc1qr35hws365juz5rtlsjtvmulu97957kqvr3zpw3

Did you use RBF or CPFP on any of the transactions for depositing into your casino account? I was never any good at investigating blockchain data, but here is what I noticed after a quick glance:

https://mempool.space/tx/e026d94285ec58ef1ade9da48b4a9c80ea481feae10db8bd174c2ec25b5b48a5 - someone seems to have made a CPFP to bump the fees of this transaction which also involves your casino account. Do you know anything about that?

Like I said, I am not a fan of investigating blockchain records, so someone who knows this better than me should probably take a look. Perhaps that causes the issues and what they consider to be a doublespend!?