GamingCuracao doesn't have an official complaints portal on their website like other curacao license providers (ex. Curacao e-gaming). That email address is useless as they never answer any email you send to them, I've tried in the past with other bookmakers.
One option now would be to hire a lawyer who specializes in such cases, who would then also take over the official communication with the casino. However, this will definitely cost (a lot of) money and, if you don't win the case, would probably end up being very expensive - unless you happen to have legal expenses insurance or something similar.
However, it would definitely be worth a try; many lawyers also offer free initial consultations.