From what I know this connection exception is caused by the Bungeecord.
Connection refused = The server didn't allow you to connect.
No further information = There are no additional informations about the exception.
Thus meaning the error might be on your side, probably caused by your network settings. And as everyone would say: Check your firewall, check your internet connection and try restarting your game. If the error still persists it may be on the server's end. Including, but not limited to one of the default spigot servers you are trying to connect to (Hub) is down.
Hope this will help you.