May be chess.com team just blocks cheaters, spammers etc. Sometimes it can be pretty easy to bust a cheater who always plays first engine line 
If you think that they have blocked somebody for no reason then try to contact support team, I don't really know what else can you do about it.
Professional Chess.com Blockers
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Chess is a game about love.....but we have so many professional blockers who hid behind the ability to block people....Precious individuals who live in a bubble........