Welcome to ASC!
iCloud: Advanced Calendar and iCal troubleshooting will provide you with a step-by-step procedure to help solve your problem.
If that is not successful, try posting a new question in this Forum, detailing the steps you have taken.
I too have duplicate entries in iCal on my iPad after syncing my iPad to my iTunes from my Mac, however, my iCloud has been off, so that doesn't appear to be my problem. Also, under info advanced in my iTunes, my calendar and contacts are also turned off, so that can't be the problem either. These were two suggestions that were previously suggested, but has not solved my problem. What other suggestions does anyone have?