leetsomthing:tell me his avatars name and my guild and i will mass defame him, if hes pro tthan ill get my buddies guild
One of the WORST solutions to use as it doesn't help fix the problem at all. Rather it'll escalate it and he has the right report you and your whole guild for harrassment.
As for the problem, have you tried to log a ticket with nexon? If you haven't do that and provide screenshots. You can also record your game play and put it up onto youtube and send nexon the URL to them.