CasinoGuru does not mediate sportsbetting-related cases. They will not handle the case.

AskGamblers does mediation to sportsbetting-related cases, so yes, [to answer OP's question above about sport betting branch] they have that "branch", but apparently sportbet.one is not on their list.

I initially suggested a mediator because I take a quick look at AG and found sportbet is on their list. I didn't take a deeper look into their page. Upon looking at them just now, it came to my awareness that not only it's sportbet[dot]com [not [dot]one], it's also terminated from AG due to the lack of response.

There are other gambling ADR bodies besides AG and CG, but I also didn't find sportbet on them.