Can the current company hold my salary?

I worked in a company for the past 11 months. As I have got a better opportunity in another company so I have resigned in February 2015. I've completed my notice period of 2 months (April 2015) as mentioned in my offer letter (received at the time of joining). But after submitting my resignation letter, the company HR officials are informing that notice period has been updated to 3 months (officially there is no written document of 3 months signed by me) for all the employees. Anyhow, they have accepted my resignation and asked to complete the notice period of 3 months. But after my discussion with my HOD, they have accepted to relieve me on 7 of April with all procedure. At the end of relieving day again, I got information from my officials that I have to complete my notice period which was up to 30 April 2015 (i.e. more 23 days). As of now, they have held my salary of 2 months and all required relieving documents. Hence, I kindly request to suggest me with the best solution for the above discussed matter so I can have my salary and all documents back and join my future copy without any hurdles.