Usually it's all just hot air.
They can send a lawyer after you, who will intimidate you a little, but that's all. The important thing is not to sign anything they give you.
If you threaten legal action, it's just hot air. They have to justify their legal claim in court, but they can't do that if the transactions were intended for illegal gambling.
Important:
As a precaution, save evidence, save it on a USB stick, and make sure that the transactions are related to the casino. It is best to save the casino transaction history with the date and time. This way you can later compare the transactions from the credit card with those in the casino.
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