How to update other users shared calendar via command line (cadaver)

we’d like to transfer users events from a internal calendar system to the nextcloud calendar.
So we create one special user ‘company_user’ and every nextcloud user shares her ‘company_calendar’ with this ‘company_user’ in read/write mode.
The thought was, ‘company_user’ connects (using cadaver) to every user account and puts/deletes events.
The problem is, this seems to work only partially, ‘company_user’ may create a new event in 'user1’s calendar and this event even appears in user1’s calendar in nextcloud web but ‘company_user’ may not overwrite this event neither delete it. When I connect as ‘company_user’ in nextcloud webinterface, the imported event is not shown in user1’s shared calendar.

Does anyone know a way to batch-import other users events in nextcloud? Sorry, I did not find another way in the net after searching for hours.

NC 12.0.3
CentOS 7 r1611