Many times, especially with betting pattern, they are guessing.
this is the case most of the time (at least from what i have seen), especially when they ask you to snitch the other account usernames.
unless sportsbet has solid proof that he has multiple accounts, it will be his word against theirs.
like how exactly can OP prove he only have one account? it's impossible.
While it is hard for me to believe that sportsbet.io would scam anyone for $2000, I do understand that every individual case must be decided on its own merits. As of now, it is clear that sportsbet.io has suspected some financial patterns from the deposits (linked wallets, similar transactions, etc), now since OP has not shared any wallet address or txID and considering how openly the casino in question came out in public to make their stance clear, it shows that they have ample proof (my opinion only from experience).
OP, can you share your wallet address? If you believe that this is a mistake on the part of the casino, please advance your case to any reputed third-party mediator.
Since I don't charge, it is somewhat irrelevant where I deposited from (Binance), I had lost the last bets, the last time I won I had deposited BTC and I had charged to the unique address that Binance gives me to receive BTC. I still share the TxID of the ADA deposit that I made to them: