"Unable to connect to the proxy" error
First of all please check if your proxy is active and don't expire on the site where you have purchased it.
If the proxy is active and has not expired, please check that your hoster doesn't block outgoing traffic to a specific proxy port. Most hosting providers are blocking outgoing traffic with their internal firewalls.
To check if the proxy is being blocked by your hosting company try to add using the proxy to the system in Administrator -> Proxies -> Create new proxy.
If you got a "Can't connect to proxy" error and sure that the proxy is 100% working, then it's a firewall limit. You need to ask your hoster to allow you to use proxy and connect to it.