Don't worrie we don't think you cheat just because someone says you did. We watch demos on a regular basis to catch cheaters on our server among other things.

As far as Unreal goes here's a couple things you can do.

Simply tell him to go fuck himself, or stalk him in our forums.

Make an anonymous account (or use your real one) on the forums and post a rant about Unreal.inc in the dicky people forum - that's what it's there for :)