It's common not to allow multiple accounts and even to void winnings once they discover another account. I can see that you're frustrated but I what do you expect to do? You can't have multiple accounts and it's stated in their T&C's.
Players are allowed to have only one account per household, shared computer, physical address and or internet connection. Players using false or misleading information during registration will have their accounts closed and all winnings will be forfeited.
If you've played there over the past few years, how have you managed to cash out before? Have you recently opened another account?