FNF issue - HR saying that I had to apply for FNF within 30 days and now they can not do anything

I was working with a company from 27 June 2014 till 25 march 2015. On 25 March I have given resign to my manager and her superior. They accepted the same. But nobody told me to meet her. So after 45 days, my FnF did not come. So I contacted the hr and they r saying that I had to apply for FNF within 30 days and now they can not do anything. So what I can do right now

As I understand you gave resignation to your manager and her superior on 25th and left the job.
Has your manager given an acknowledgement of your resignation letter to you?
What does your appointment letter/job offer speak about notice period/buying of notice period etc?
The excuse of the company that you have to apply within 30days is just a company procedure and they cannot deny you FNF because of that factor alone.
Did your company speak about notice period or they have accepted your resignation?
In your resignation have you asked for full and final settlement also?
What capacity were your working and in which industry?
Depending on that you can approach the local labour officer for delay or refusal to clear your dues.
One needs to give more information to get clear advice from members.

My resign was accepted and they told me that I'll get my fnf after deduction for notice period and I have excellent performance record over there.but I don't have copy of resignation letter.company is Bpo with good count of manpower