In these cases it's always statement against statement. Without seeing evidence it's hard to trust the casino. They make the accusation, OP's words here are just a result of that. So they need to show proof. OP cannot proof he doesn't own multiple accounts or what not. They are holding all the evidence.
The representative of the casino has accused OP for 3 reasons. The casino team won't post the multiple accounts related evidence in a public forum as it goes against the security of the platform. But both OP and casino team have the ability to post the betting history of OP here. We will be able to verify the 3rd claim against the user if any of them post the full betting history.
This is completely false - I've never ever had an account with you nor have I "bonus hunted".
I think it would be better for you to reach a mediator to verify you have only 1 account there. Sportbet.one has been
reviewed by Casino Guru, you may submit a complaint there. BTW, they will only look into the multiple account related matters as they don't provide services for sports betting related issues.