There is a thread on here called Crysis 3 hacking. The man you want to talk to is Fellblade, tell him who it was you suspect hacking, the date and time it happened, as well as what server this was on. If you have video evidence that is even better. There is another thread on this forum that gives links to some free capture software that you can run while playing Crysis 3 in case you find any suspected cheaters. I'll try to find these links for you before this thread is locked as the forum rules are to not "name and shame".
Fellblades post including instructions for how to report cheaters. Mainly it involves sending him a private message containing the information I provided above.
http://secure.gamesas.com/forums/viewtopic.php?f=65&t=59890
And here is another thread with links and comments regarding free capture software for PC users.
http://secure.gamesas.com/forums/viewtopic.php?f=65&t=64030