Like Freddie Mac, Fannie Mae has an online facility to ascertain whether Fannie Mae owns your mortgage:
Fannie Mae Loan Lookup
I have not used this facility. I would be interested in hearing from anyone who has succeeded in looking up the status of their property and whether they found the information useful.
The comparable Freddie Mac facility is discussed within MS Fraud Forum message thread:
Does Freddie Mac Own Your Mortgage?