Getting "MICROSOFT SUGGESTIONS" in my Outlook Calendar that appear to be spam

Do you use outlook desktop? (It's easier if you do.) 

if the events were over written, they are gone. If they were deleted - you can look in the deleted items folder in outlook desktop - in the Folder list view (Ctrl+6) - turn off the reading pane and sort by the icon. 

If they aren't in the deleted items folder, they might be in the recovery folder linked at the top of the deleted folder. 

It's easier using an Office addin called Email Recovery. It can recover mail that is in the recovery folder or in the purges folder.  It creates a new folder for all of the recovered items, so you don't pollute your folders with old items. When done, deleted the folder then delete it from the deleted items. 

Email Recovery (microsoft.com)

The suggested meetings addin (which I thought was now defunct - its long gone from my accounts)  doesn't automatically add events to the calendar - it just suggests a meeting. It, Bing Maps, and My Templates are default addins Microsoft includes with all accounts. 

This link shows how it works, but the screenshots are from an old version of Outlook on the web. 

Installed add-ins - Outlook (microsoft.com) -

Can anyone help how to recover the events that existed in the calendar? Because mine were erased or overwritten.

I figured it out. On the right side of a message with a suggested meeting, click the Get more add-ins link. Then select My add-ins and disable Suggested Meetings. I never enabled this by choice, not sure why the default is on. Bing maps was also enabled automatically on mine.

These messages are meeting spam added to the calendar as tentative appointments,