If they persist via msg or dcc, you can put them on ignore. Some IRC clients allow for specific types of ban by adding a parameter. See the help file for your IRC client for details. Each IRC client handles ignore a bit differently, so check the help file or FAQ for more information. If the flooding is in channel, you may want to ban and kick them as well.
Clones are multiple simultaneous instances of the same user.
This may get you some attention from a StarLink-IRC representative, but is nothing to worry about as long as the situation is temporary. A kill disconnects a user and is equivalent tothe kick command. A gline is a special service that, in effect, bans a user from ALL StarLink-IRC servers. It is possible that you may connect to StarLink-IRC and find that 'you' have been banned from a server. Sadly, when some people become very abusive running clones and flooding, we have no choice but to ban them from the net.