Hi marktg - welcome to ThePOGG.com!
Before we can do anything to help you I need you to provide me with the username and email address you use at Bovada.
I also need to know the dates of play and why you felt it necessary to use a VPN when accessing Bovada? In general using a VPN when accessing an online gambling operator is activity that is strongly associated with players who are either a) trying to hide their identity to assist with the operation of multiple accounts or b) accessing from a jurisdiction they shouldn't be. In either case this is behaviour that the operator cannot allow.
This goes so far as having terms specifically restricting this activity as can be seen below:
"6.2. Fraudulent Activity.  If, in our reasonable discretion, we determine that a player has engaged in fraudulent, unlawful, dishonest or improper activity (including, without limitation, the usage of a VPN, proxy or similar service that masks or manipulates the identification of your real location, or by otherwise providing false or misleading information, or by making bets, wagers or poker play through a third party or on behalf of a third party) we reserve the right to immediately terminate or deny a player access to their Account. In such event, all Account balances (including both deposits and any winnings) shall be forfeited and we reserve the right to disclose information (including the identity of the player) to applicable parties including but not limited to; the Gaming Commission, banks, credit card companies and/or any person or entity that has the legal right to such information, and/or taking legal action against such player."
Ultimately, having admitted that you have used a VPN, you have broken the above term and Bovada are within their rights to close your account and void your winnings. While I can speak to the operator, essentially there's no grounds to demand the return of losses and anything that they do will be done in a 'discretionary' manner - i.e. there's no assurance they'll do anything to help and if they do it'll be based on convincing them that this was an honest mistake.
Thanks,
ThePOGG