Maybe they are investigating for signing up multiple accounts? I would just try avoiding VPNs at all costs.
This is what I found in their TOS:
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 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.'
Good Luck