I'm not a US resident but they also do the same for me. I can't withdraw anything. They basically stole my money. Their support did not reply.
If you are not US resident then why dont you try to verify your account??
After verify so you can withdraw your portofolio.
Is that so hard to verify?? As i know in the other exchange they need scan of identity card, scan of utility bill and might be verify phone number. I dont know what they need in bittrex.