The 24-year-old singer - who previously had a five-year on/off romance with the 'Sorry' hitmaker - told her former beau to stop uploading pictures of him with his current girlfriend Sofia Richie if he "can't handle" being criticised for his posts, and urged him to not take his anger out on his fans.
The brunette beauty commented on a picture of the couple posted to Justin's Instagram account, which saw him threaten to quit social media.
She said: "If you can't handle the hate then stop posting pictures of your girlfriend lol - it should be special between you two only.
"Don't be mad at your fans. They love you. (sic)."
But Justin then appeared to hit back at his former lover for "using" him "for attention".
He wrote: "It's funny to see people that used me for attention and still try to point the finger this way. Sad. All love.
"I'm not one for anyone receiving hate. Hope u all can be kind to my friends and each other. And yes I love my beliebers (sic)."
And Selena then appeared to take another swipe at the 'What Do You Mean' hitmaker by sharing a collage on social media of her interacting with her supporters.
Alongside the picture, she wrote: "My whole life. You matter most. Thank you letting me do what I love every day."
The war of words came after Justin, 22 announced he would make his Instagram account private if the abuse directed towards his new girlfriend continued.
Speaking previously about quitting the photo-sharing website, he said: "I'm gonna make my Instagram private if you guys don't stop the hate this is getting out of hand, if you guys are really fans you wouldn't be so mean to people that I like. (sic)"