iMac Contacts not syncing with Office365 Exchange

Hi

I have an iMac at home running El Capitain 10.11.6

At work we had an Exchange server Exchange 2013. My Mac was quite happy syncing outlook mail at work to mail on my mac; contacts from outlook at work to contacts on my mac; and the calendar from outlook at work to my Calandar app on my Mac. All these things also synced fine with my iPhone and iPad

I have just updated my work systems to now use Office365 in the cloud, including Exchange on Office 365 running Outlook 2016. I added the new 365 Exchange account to my iPhone and iPad and they sync fine. I added the new 365 account to my mac and whilst Mail since fine, the calendar App and the Contacts app will not sync .

I have downloaded Outlook for mac from my 365 account - and that syncs fine on everything. But Outlook for Mac is really poor in my opinion and I prefer to use the mac apps of mail, contacts and calendar

Any ideas on how I can get calendar and contact syncing again please?

Details

To add the new account to my mac I chose Exchange, entered my Office365 email address and password and pressed enter. This was all accepted fine

When I open Calendar, I can see on the left panel that the Exchange account calendar is there and ticked. But it has a grey triangle with an exclamation mark in it and no calendar items are synced. The error message I get is "Calendar items cannot refresh events in the calendar "calendar" There was an error attempting to send your changes to the exchange server.

When I look in my Contacts app I see the All contacts account from Exchange listed in the left panel - but again with a grey triangle with exclamation mark. The error this time is given as "The operation couldn’t be completed. (SOAPWebServicesErrorDomain error -997.)"

yet email syncs to Apple Mail app without issues. And as I said, my iPhone and iPad sync contacts calendar and mail fine - using the same office365 credentials to set up the account on those

Any ideas please?