Since you have already passed the exam, your file must be at your local office so try to contact them. I have no idea how to find their phone number but you could go there and ask them in person. You could also call the call centre, see http://www.cic.gc.ca/english/contacts/index.asp but if you can not find out this way, make an appointment with your member of parliament and ask him or her to find out for you what is going on or to push a bit. What does your eCas status say?
I also had to wait over 2 years but not after the exam, before the exam. I had applied for citizenship and got my AOR fairly quickly and then had to wait more than 2 years to be called for the exam. After the exam, I was called for oath fairly quickly. I was not in any hurry so I never asked why it was taking so long. I was never asked for more documents. My eCas status was always "In process". I was starting to think they lost my application and possibly they did. Maybe it fell behind a cabinet and was found like a year later. Maybe a similar thing happened to yours.