I-797 Approval notice not received..

Hi all

Latest update on my case- 

1- Case was filed on 14-nov-2011 in regular processing. USCIS site show status as initial review. Case is pending since 9 months 
2- we upgraded the case into PP on 23-july-2012. Still no update in status. it is still in initial review. 
3- When my employer checked with uscis he came to know that case already got approved in march-12 itself and he did not receive any approval notice from uscis. 
4- As per employer uscis has never sent approval notice on my case. He suggested that he will ask them for duplicate approval copy. 

My questions here are- 
1- How we can get duplicate approval notice. Is there any extra fees for it? 
2- Is it possible that uscis forgot to send approval notice for particular case? 
3- How much time it will take to get duplicate approval notice?