On one hand, Rollbit claims you have other accounts, while on the other hand, you strongly assert that you don’t. I’m not sure how the community can resolve this kind of issue since both sides are holding firm to their claims.
Maybe Askgamblers or Casinoguru can be of help. But I do not really know about these sites.
Op have you ever used a VPN to access the site? Most times issues like this can arise when you use vpn especially free VPNs.
Issue like this arise when someone's IP are connected to other accounts. It might not be the use of VPN. If it is the use of VPN that Rollbit do such a thing, it is better you avoid the site.