I'm not saying that I believe OP's story, at the same time am not siding with the casino, but in such cases, it's really difficult for the accuser (OP in this case) to prove his innocence. What kind of proofs do you think he can provide to support his case? How can he prove he doesn't have any alt accounts?
In such cases, the best thing to do is to refer to an independent mediator such as casinoguru or askgamblers then each party can submit their proofs and tell their side of the story.