Today I deposited some funds, played a few games and began to lose so I tried to make a withdrawal.
Have you ever read their ToS? Many casinos have an anti-mixing rule and will not allow you to withdraw if you have not met certain wagering requirements. In addition, it is becoming more and more common nowadays to put in the ToS that you may be required to KYC.
1. Curacao registered site
What do you mean? Most of the ones advertised on the forum are licensed in Curaçao and I have played on several of them for some time without any problems.