all ISPs in Singapore make you access internet through a proxy server. It is this proxy server's IP address that is causing you the problem.
For your proxy IP, please go to
http://www.showmyip.com/, and scroll down to the section on "Proxy properties". That "proxy IP" is your IP address as the rest of the internet knows it.
You "actual" IP address is only an internal IP used by the singnet server to keep track of where to forward the data from the proxy server from. To the rest of the internet you don't exist at your "real" IP, only the proxy IP matters and that's why you are unfortunate to be blocked because of a vandal who was/is sharing the proxy server with you.