Lost Cd Key Number For Unsupported Ms Office For Mac

I have MS Office for Mac that was 10.0.0, and I made the sad mistake of trying to upgrade it so I could end up adding the patch for openning the newest Office or Word documents.  Once I installed the upgrade, the program asked for me to re-input the CD Key number.  I no longer can find the disk or the box for the item that had the CD key number needed--we moved and the box disappeared somewhere.  When I called the Microsoft help line they said the version was no longer supported, so they could do nothing for me.  Before I openned the program to upgrade the 10.0.0, I did read the ReadMe doc and it said nothiing about having the CD key number ready to re-input once you have the upgrade completed, so I am really frustrated with Microsoft.  At least they could have had the courtacy to have noted that on the ReadMe.

I'm going to see if I have the old version on a back-up somewhere and see if I can go back to the old version. 

Other than that, is there anyone out there who can help?