Unable to update calendar.

My Calendar (IOS18) will not update on my iPhone 14Pro. MacBook shows new appointments as they come in (tested with my Tidycal bookings calendar and it came in as expected, iPhone - still nothing)

After searching the community and elsewhere I have turned off the calenda, then back on again, checked the connection, checked the default calendar. Checked its syncing....all the things! I then turned off the calendar allowing it to delete all entries, rebooted the phone (again) and turned back on the iCloud calendar. My calendar still won't upload and now my entire calendar is empty!!! this is a major disaster as my phone is my main diary. I don't 'carry' my MacBook around with me and rely on the phone to keep my day straight.

I have now updated to IOS 18.7.1 and still no calendar. Help!