Who cares what he thinks, tell him to pop some zits
A properly set up server that you play on "should" have a mutator that can prevent any type of hacks (like a cheat hack). If the person that accused you of cheating IS running the game server (very unlikely), move on and find another safe server. The bottom line is; unless the server has such a mutator, there is nothing you can do.
FWIWThe CSHP2 mutator is something every server should be using. It will automatically detect and kick a player/user that is trying to exploit the security flaws in U.T.