Legal Resort for Relieving, Experience letter after serving notice period if employer is reluctant?

I was working in my current organisation from last 6 months, Here there is a commitee with Director and 4 secretaries and members who take decisions in form of monthly meetings. Meetings minutes are documented as proof. My appointment letter mentions my appointment is for 6 months period and in last month meeting my term was extended for two months. I have given my notice for resignation promptly but they are reluctant to provide me relieving letter. Also there is no salary slip given by the organisation.I have been selected in new job and have committed to join it after completion of notice period along with relieving letter.Also, I need this letter as it is very important for my career to prove i have completed 1 year in my field and the position was also big. Without proper relieving and/or experience letter no govt. agency recognizes my work experience. Please suggest legal resorts as the organisation is aided but has very unprofessional administration. They haven't given proper relieving to many ex-employees.