Depends on which game. If it is a Sony-published game, then use this page...
If it is a third-party game, then you have to report it on the game's support site. Sony will not generally pass your report on to other publishers, and Sony will not take action against a user for something that no Sony employee has seen.
@CodedMendez, gkpama00 information is correct but there is a flaw [loop behavior] on the report link found on the report article. To reach the complain form, follow this link https://us.playstation.com/community/feedback/
At the bottom under "What is the nature of your comment?" select "Complain" and type your report away.