Deleted Event from recurring Webinar series still shows up in Calendars

[CandisGmbH]

We have a monthly recurring Webinar series scheduled. I made two changes that are not showing up in our connected google calendars. 

1. From this series we had to cancel 1 event.
   I deleted the event from the series, however, it still shows up in the Google Calendars of my colleagues. We are now worried it also still shows in our customers calendars. How can I deleted it from all calendars? 
   
   
2. Changed the date of the series 
   We had to change the date of the series, from every 2nd Tuesday of the month to every 3rd Tuesday of the month. This change is also not being reflected in the Google Calendars. The next event still shows on the 11th June instead of the week after. 
   
   Please help!