Well.. i checked for irc.rizon.net:6667 here
http://ping.eu/port-chk and it says it's open.
Something that has happened to me long ago was that i made a lil typo that i didn't notice for some hours.. so i couldn't connect.
Other possibilities:
Maybe you're using mobile internet and they've banned the IP? (3G, 4G)
In case you do.. the IP usually changes if you turn off and then back on the mobile internet.
