Mempool.space mentions CPFP in its records for one of your past transactions, which is perhaps what the casino meant when they mentioned doublespending to you. Ask the support which transaction was doublespent to see how they will respond.
But I'm not sure how a CPFP could be taken as suspicion of attempting to double spend.
Because you're not replacing a transaction/spending the same input/s. Instead, someone who owns an unconfirmed output from the parent transaction spends it in another transaction with a bigger miner fee covering both of them -- child and the parent.