It's common. Just ignore them honestly.
People cheats and accuses their opponent.
But calling them out on chess forums isn't the smartest idea as chess moderators have stated that no discussion of cheating is allowed and so is exposing their username...so I don't know how this will go.
I have locked this topic as it accuses other chess.com users of cheating. Accusing users of cheating is a violation of our Community Guidelines.
On the user's profile is the option to "Report". You can report the user for cheating or other violations. I hope this helps.
[Moderator removed accusation of cheating - AA]