cheat

Hello, my name is Hakan Özgök. I am writing you from turkey. I want to report you a scam. but I don't know where to apply., dear official, I am requesting information from a company of Chinese origin.  I would be very glad if you can help.  I started trading dollars at 'Cowtrading wealth ltd' (https://www.cowtradingvip.com/ ) through a Chinese close friend.  But when I wanted to withdraw the dollar I deposited, they demanded dollars under the name of tax.  I paid, they asked again, I paid again.  But they are still requesting dollars and not transferring back the amount in my account.  Which institutions or organizations should I contact about this issue?  Can you help me