Denied Withdrawal

I made an investment of 52,000 US dollars with Capstone. As at February, I had made some considerable profits which I tried to cash, My three applications for withdrawal have been rejected and then the broker asked me to pay taxes, handling fees, etc. At first I was sceptical but I still went ahead to pay the fees after their support assured me it would be all that's required. Things went from bad to worse when the support stopped responding to my mails, they wouldn't process my withdrawal either.