Casino often delete game history that happened few days ago if you are active on betting. You can request it to their support if they have backup but I experience same thing on other casino that I’m playing. It’s not a good proof that they are cheating by hiding your bets
If their intention is to scam the user in the first place giving the user the record they are finding for "backup" is impossible. But since there is no enough proof to back this up by OP i wonder how he will succeed to this.
OP claimed that he meticulously documented data. Bets, outcomes, hashes. He should be able to provide and verify some of those bets himself to build a back-up evidences for his claim