I believe that, with the presumption that it's a false-postive/you don't actually have other accounts, ask them why they're saying that you have more than one account? 🤔
Plus for those users that actually do have more than one account, but have not done anything nefarious in the casino, I believe it won't be a big issue to admit and list those other accounts.
If the user did not answer to Rollbit's request, it is like a case is closed at least from Rollbit side. The user can complain whenever he want but until a time he submits required information to Rollbit, his case won't be reopened and investigated again by Rollbit team.
That's why proper cooperation is important and if he didn't answer on Rollbit's request then expect that he won't really get a response in return. I guess he just need to prove that he's not using multiple account and its time for Rollbit to release their proof since for sure they have reason on why this situation happened.
Also for sure that they won't do same action if they know that particular gambler didn't violate their rules since their reputation will get destroyed if they do that.
But still hoping for the best that both parties would settle up and this situation will be solve in future.