https://support.chess.com/article/648-what-do-i-need-to-know-about-fair-play-on-chess-com
If you feel a member may have using disallowed resources, you should just report them directly to staff.
https://support.chess.com/article/209-how-do-i-report-someone
Discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums.
If you would like to discuss, without naming the suspected player, you can do so in the following club.
https://www.chess.com/club/cheating-forum
I played a user who sac-ed his queen on move 17 instead of simply losing his bishop.
I eventually resigned on Move 40.
I analysed the game on the popular open-source website and he had an 86% accuracy.
How can I be sure he was cheating?
I've attached the game below.