outlook 2011 for mac duplicate calendars

I am using outlook 2011 on an iMac.  When I first bought it a couple of years ago I imported my PST outlook file from my windows laptop.  Instead of adding the information to the default 'on my computer calendar it created a second calendar under another 'on my computer' heading with the name of the backup file.  I wasn't really aware of this at the time.

When i discovered I had two calendars I tried to work out how to merge them or delta one, but could only delete the one that contained my back up info. I couldn't work out how to merge them and so finally just kept working on the imported version as I couldn't delta the default calendar the one without all the my information in it  Then I bought an iPhone and an iPad and tried to sync my calendar with them and yet another version was added causing more problems.   For  a while things got very confused and it was pot luck which calendar new information was saved in unless i was working in outlook.  

I have just signed up for a Microsoft exchange account with a new domain and email as I was  told I could then work on my outlook calendar via the outlook web app and no longer have the problem I was experiencing with syncing.  I have turned off the apple iCloud syncing for my calendar on both devices. 

I added my new exchange account and of course it created yet another calendar in outlook so I now have 4 calendars!    I have spent hours online trying to find a solution and also on the phone with our success.   If i try to export my calendar it only exports the data in the default calendar - which is incomplete!   If I then try to import it it adds yet another calendar!!!!   

My calendar entries go back to 2009 and it is important that i keep them as they are work related. Please can someone tell me how I can get  ALL my calendar data from the correct calendar into my new exchange account calendar?  How do I back up the calendar version i need and not just the default one i don't get an option to choose.   Or can i somehow assign the default calendar as the exchange calendar and get my data into that one instead?   I'm loosing the will to live at the moment as it seems to be a mac related issue. 

I was going to reinstall outlook but having discovered i can't back up the calendar version i need I don't see how to do that.   I found lotos of suggestions for windows based version and none for the mac version.