icloud calendar update conflict

Dear all,

need your help, please. Since a while i have big troubles with my icloud-calendar. Using it on iPhone, iPad and my mac (mojave).

I can't delete ONE person a shared my calendar. This person was a former worker in my company. Still not anymore working for us. I want to delete the share, but i can't in anyway, not at iPhone, not at iPad, not at Mac and even not directly on the icloud!!

I already deletet the cache of ical at my mac, cause first i thought its a mac subject, but since now i know, it isn't... cause i can't delete it on the icloud directly.

Today on icloud i received the following message:

"Dialog.Error.Single.Title.Participant.UPDATE

Dialog.Error.Single.Text.Participant.UPDATE.CONFLICT"

Is there anybody, who can help me out here...

MANY THANKS !