@media screen and (max-width:767px) {
  .oc-chat {display:none!important;}
}


i gave this code at style.css its worked successfully but when i try to click online chat button below the description listing(online chat button) then chatting terminal will not opened   

@nijamutheen
reason is that code you put into your style.css hide chat block.

Also i have this problem , i see chat button , when clik button , chat window not opened ,

How to resolve this ? What is the use if happened like this means

@nijamutheen
Remove code you've added, problem is resolved then.