My dad was scammed by VIP TRADER

My dad had invested 20000 USD and until today they refuse my withdrawal. The broker VIP Trader refuse to withdraw unless another 5000 USD is added into the account. To be able for us to withdraw the money my dad pay $5000 and we try to withdraw the money from my dads account but we just disappointed because we never received the money.This is total scam company. Many times we tried to call but nobody answer or line disconnected. How should I solve this problem?