Some people disable chat. Some people ignore it (probably not even knowing it is there). And there are many kids here too who are probably well advised not to react to any messages from people they don't know.
But when they do respond and are rude, report them. Not much else you can do.
I've been on chess.com several months. I haven't seen one good sport out of several hundred games. If its a good game I say that even if I get beat. I have never had a reply back. Any time I accepted chat it was always rude - sometimes extremely rude. I play a lot of FPS and it is far more friendly. I guess at my newbie level I shouldn't expect more. When i get to 1200 hopefully it is people are better sports and can recognize good competition.