our internal tracing methods go deeper than just VPN usage.
When it comes to reputable casinos it does not make any sense for stealing a mere $500 from a contest winner. You might be not aware but let me tell you that casinos are so good in detecting multiple accounts. In my limited knowledge (I can be wrong) I can say that no reputed casino will confiscate your winnings just for using a VPN. As per my inference of your case, casino in question is accusing you of exploiting the giveaway by making alt accounts via not only your IP logs but/browsers/devices/patterns etc. and they seem quite confident in their claim.
Right now the only option for you is to open a case with mutually agreed third party mediators as no casino will publicly post such details (IPs etc.).
