Sometimes people get upset with you for their own reasons. I once had a friend stop talking to me and I had absolutely no idea why . Some of these answers are pretty harsh. Also there is NOTHING you can do to make another person do anything. But you can say ( or message) that you care about them and that when they are ready you'd be glad to talk things through. If you owe them an apology then apologize. If not, and they still don't talk to you , mourn your loss, remember the good times and move on to other ( better ?) friendships. Perhaps they just need their space. Do something nice for yourself while you give them a breather. Good luck.