Calendar not syncing across devices

Hi there, my calendar is no longer syncing across my devices -- iPad, Macbook Pro, iPhone 7. Nor are changes made to it on iCloud showing up on my devices. I have tried everything! I have deleted most of what is stored on iCloud. I've shut off and then on calendars under "Apps using iCloud." I have rebooted all devices. All have up to date operating systems. What gives?