Calendar alerts function does not work

IPhone 7 Plus; iOS 11.2.6.

I create a calendar event and set an alert for "at time of event" or any time in the future. No sound comes. I have searched this problem on Apple Support and followed all suggestions. Go to settings/notifications/calendar and make sure Allow Notifications is turned ON. Go to all 5 events, Badges, Sounds, Banners and make sure they are all turned ON. Go to settings/sounds & haptics/calendar alerts and make sure a sound setting has been chosen. Go to settings/calendar; Show Invitee Declines is ON and Location Suggestions is ON. I have turned the phone OFF for several minutes and that does not work either. I hesitate to re-boot the phone since I may loose all my custom settings. What else is there to do? HELP.