Delete event only when logged in icloud.com
Some events are added to your iCloud calendar, and you cannot then edit it directly on your iphone/ipad as usual (by editing or modifying the event and going down to the red button remove), you need to go on icloud.com -from a Pc or Mac, not from your ios device, and log in, and select the calendar icon: select the event you want to remove, and in the pop up window select "refused" instead of "accepted" (not sure if this is the correct words as my configuration is in French). this will remove the event from the calendar you have on your iphone/ipad ...
Some events are added to your iCloud calendar, and you cannot then edit it directly on your iphone/ipad as usual (by editing or modifying the event and going down to the red button remove), you need to go on icloud.com -from a Pc or Mac, not from your ios device, and log in, and select the calendar icon: select the event you want to remove, and in the pop up window select "refused" instead of "accepted" (not sure if this is the correct words as my configuration is in French). this will remove the event from the calendar you have on your iphone/ipad ...