Block access to the site by anyone using VPN or ip Changer software.only real ips allowed

Block access to our voice chat site(its a 123flashchat) from all vpn and ip changer softwares and fake ips. I have seen another site based on the same script(123flashchat) that when you try to access using vpn or ip changer software, the chat does not load while the rest of the site do. it would be a good idea if the user try to access the site using a vpn or ip changer software and they get a message saying they cant access the site because they are using a vpn .