Contact a conressman
Bindaas, I suggest that you contact a local congressman or, better yet, a senator. This was the only thing that helped in my case, as I was in a similar boat. My I-485 was approved by NSC in March 2002 and that's when I did my first passport stamping in Chicago.
It took exactly two years, before my card was finally issued in March 2004.
Apparently my original I-89 documents were lost, most probably in Chicago.
Both Nebraska and Chicago repeatedly lied and provided misinformation in response to my requests, and then stopped replying altogether. In July 2003 I convinced the Chicago CIS office to redo my I-89, but that did not seem to help since between that time and March 2004 I did not hear anything from CIS. Finally in March 2003 I wrote a letter to senator Durbin from Illinois. His office got actively involved and withing about ten days from writing to him, my card actually arrived. Interestingly, after that NSC "discovered" all my previous G-731 inquiry about the status of the card forms that they had been ignoring earlier, and during the next couple of weeks I received responses to all of them (they all said "our records indicate that your card has been mailed to you..")
If your I-89 documents (the so-called "signature card" with your photo and fingerprints that is prepared at the time of passport stamping) were also lost, my experience shows that it will be very hard if not impossible for CIS to rectify this problem by itself. So outside intervention is advisable.