@rjun
I guess you just scanned a site which has c-panel installed , and also you might have seen p ftpd port open among others and you wanna log in as admin by brute forcing ftp w/ hydra And use the same conditionals (found by hydra) to log in to c-panel.

You need to understand a single proxy can't help and may not even multiple ones if you got them for free though. check http://proxylist.hidemyass.com/ and "Google it my friend you would find plenty"
No need any a/c for free proxy just punch in "ip:port" and you are ready to go.
But it's not quite a safe or anonymous way i won't prefer it.
The problem is there exists a time-delay windows which blocks brute forcing after a certain number of unsuccessful attempts in the given time. so you need to guess the delay time and use it shrewdly in Hydra.
                            Otherwise what's happening w/ you that  you are not the only one who got blocked after a certain no of wrong attempts. Infact the whole ftp  server stops responding to login quires for a certain period and if you were using the proxy(ies)  I guess that to won't help you either untill you put in delay in b/w your attempts.

And what you can do w/ proxies that you can create a simple bash script to auto change proxies after N number of seconds. So the site admin may got terrified after seeing bruteforcing attempts from all over the world.

GOOD LUCK"