You can use the online tool to find your Representative first:
http://www.house.gov/writerep/
If you're not sure of the entire 9 digit zip code, use USPS' website.
Once you get to the Rep's homepage, you may find that that particular Rep already has a form specific to immigration issues. If not, you may have to compose a letter asking for help. An alternative is to call up their office and speak to someone there. That would provide a quicker response.
I submitted an on-line request from my Congress men website and also faxed a copy of my details to his office with details of receipt number / A# / Priority date and where my case is currently pending and what information I require on my case.
After I submitted my request I received a letter informing me that they are contacting USCIS / TSC and after one week I received another letter with information on the status of my case, unfortunately my case got struck in Name Check
PD : Sep /2002 / TSC