While I may not know of a proxy service that's available in China, I do know of a few VPN services, which will render the same end result in the sense that they will make you appear to the internet to be using an IP address from within China. The downfall to most free proxy services is that they're not an anonymous proxy, which allows them to reveal your original IP address for tracking purposes, which may be why the connection is being rejected. A VPN (preferably PPTP) on the other hand will not expose your direct IP address in any manner, thus getting around that issue.