What's wrong with my iPhone 6? - 1

My friend called me, but there was no ringtone, just a notification of a missed call. Also, it won't send any attachments and shows the red exclamation point. I have a connection. I restarted it… I even installed the latest update. I have no idea what could be the issue.

Go to settings, click on sound then follow the menu

For the no sound on incoming call n only missed called notification do this 1. Swipe up from bottom of screen to show Control Panel, tap the moon icon to turn off Do Not Disturb, that should fix it----Far as can't send attachments n red exclamation mark try resending and if that don't work restart phone

Did you turn of the ringer with the small switch on the left side of the screen, near the top. If you see a little bit of red in there, the ringer is off.