Consult with an immigration lawyer in your city so he can review the letter you received, to see if it explains the reasons why they deed additional processing.
Ok you tried to do it yourself; If it looks like there is a problem, you would be wise to shell out a few bucks for an immigration attorney. A lot of things can go wrong and only someone familiar with the process might catch the problem after reviewing your paperwork.
This is not legal advice but a general comment on society based on a limited set of hypothetical circumstances. No one should act or refrain from acting based on these comments without seeking appropriately licensed legal or professional advice. The author disclaims all liability in respect to actions taken or not taken based on his comments.