I had a similar problem, but not exactly the same. It's solved, but I thought I'd mention it here in case it happens to anyone else. I created a couple events in Outlook on my PC, which is set up to sync with my iPhone calendar. The calendar on my PC is called "Calendar from iCloud in iCloud"--not the most intuitive meaning... Anyways, I could not delete these two events from Outlook on my PC. Strangely, they were not showing on my iPhone calendar at all, which otherwise was identical to the calendar on my PC. New events I was creating synced just fine--in both directions.
I found advice that suggested deleting all events from the calendar, which I didn't think would work, at least on the two offending events, but I decided to give it a try. Sure enough, they disappeared!
But even more strangely, now those two events--and only those two events--showed up on my iPhone calendar (and no longer on my PC calendar)! Very bizarre--they had only moved from one place to another.
So then I restored my iCloud calendar from the previous day--since I now had nothing on my PC calendar and only those two offending events on my iPhone calendar. Bingo! All events were restored, on both calendars, and the two offending events were now gone.
I am still puzzled as to what happened, but the problem is solved. I wonder if turning off the syncing on my iPhone and then turning it back on would have been a much simpler fix. If it ever happens again, I'll try that first.
Incidentally, I don't think the problem was with the Outlook program, as I tried repairing the PST file (didn't work) and I also tried uninstalling and re-installing Outlook (also didn't work). Of course, it makes sense that it didn't work, since all the events are being stored in iCloud.
Lesson learned--the hard way.