Blocking should prevent being paired with the blocked member but there's a known bug being looked into by staff.
As to cheating, if you feel like another member is using disallowed resources you should report them
https://support.chess.com/en/articles/8562517-how-do-i-report-someone
https://support.chess.com/article/648-what-do-i-need-to-know-about-fair-play-on-chess-com
https://www.chess.com/article/view/online-chess-cheating
https://www.chess.com/article/view/chesscom-update-july-2024#FairPlay
The site closed almost 60,000 accounts in June for fair play violations and has a full team of staff working on reports along with some automated systems for detection.
https://www.chess.com/article/view/fair-play
That said, discussions of cheating, potential cheating, or cheat detection are not allowed in the general forums. If you would like to discuss join the following club. https://www.chess.com/club/cheating-forum
Why did I just play a guy who I have already blocked because he was cheating? Why doesnt chess.com do more to stop cheaters? The cheating has gotten out of control on this site!