There is many servers that use different proxy lookup services. The most proxies is found by these.
If you want to use a proxy. Do you know if it's socks5, socks4 or just proxy?
I saw that you found out that the channel won't accept you. I guess your proxy is blacklisted.
I have never paid for proxies before. I always used socks5 that is classified as elite proxy.
You have Transparent, Anonymous, Elite Proxies.
Easier for you would be to use a VPN instead. But sure, they could be blocked too.