Employer not doing FnF

I was working with a BPO in Surat. I worked with them for 15 months. In my CTC structure Ex gratia and statutory bonus was mentioned which my company used to pay on diwali. After leaving the organization they asked me to come for the FnF. in the FnF letter it was mentioned that I have received all my dues and now I will not raise any claim in future. I signed the letter abd written a note on the letter that I have not received my ex gratia amount of rs. .... I got a call from my HR manager who said that they will not process my FnF untill I remove the note and agree to what thy are paying. He was forcing me to accept the condition else my FnF will not be processed. They are not ready to give me in writing that I am not eligible for this amount because in none of there company policies any eligibility criteria is mentioned for ex gratia. everything is verble. when I approached the labour officer then my ex employer is threatening me that they will inform my current employer about my previous instances of misconduct, unprofessional behaviour, low performance and negative attitude towards management. These all are false. If I have done any of these They would have given me a warning letter or notice or even terminated me but they have done anything and they do not have any document to prove the same. They want me to take the complaint back and go to there office in Surat to collect the dues (as mentioned in FnF letter not full). I told them that I can not come as I am in Indore so deposit the cheque in my account but they are not ready for that also. They are saying that as per risk management policy of our company we can not do that. I know there is no such policy. what should I do ? should I go legal ?