Just as an update, my complaint has been deemed as "unresolved" by CasinoGuru as well, given that Rollbit refuse to budge or provide any reasonable explanation on stealing client's winnings.
I would caution anyone thinking of using the site to think twice, as they can confiscate all your winnings without further explanation.
Would also like to ask for any advice to move forward with this, is issuing a complaint directly with the regulator the only option?
Thank you for keeping us in the loop. Unfortunately, yes, I think the next path you can take right now will be to raise to their licensor. They're still under Curacaoan authority [previously they were with GC, now they're directly under GCB following the overhaul], however, GCB currently doesn't mediate dispute.
It will be a feature under CGA, the successor of GCB that'll centrally oversee all of gambling entities in Curacao, and AFAIK, the transition will happen in 2025. So unfortunately, you'll have to wait until GCB finally transformed to CGA to file a complaint.