Overloaded duplicates in Calendar

I seem to have remnant events from my old Outlook Calendar that are multiplying at an alarming rate. Mostly event reminders, Birthdays, holidays etc. Showing up on my iPad as repeated sometimes up to 500 times. My MacBook Pro today had 5,842 Office reminders, and when cleared, they keep coming up. Some going back a few years! I thought I had cleared Outlook when I switched to Google Mail a year or so ago, just opened it and found it was still there so I have unchecked Calendar.

I have unchecked iCloud syncing for my iPad and iPhone to see if this halts the spread.

How can I clear the duplications on my MacBook? and how can I stop them proegating the way they have? It seems it is causing a significant drain on memory usage.

I have a MacBook Pro OSX 10.8.5, an iPad mini WiFi +Cellular iOS 7.1.1 and an iPone 4S iOS 7.1.1 [about to upgrade to an iPhone 5S].

Any helpers out there, this is driving me nuts.