未読無視みどくむし口語ignoring a text message by leaving it unopened and marked as "unread" (in online chatting)
既読スルーきどくスルー口語leaving (someone) on readreading but not responding to a text message (in a chat application)
既読無視きどくむし口語leaving (someone) on readreading but not responding to a text message (in a chat application)