Regarding Gratuity

Dear Sir/ Madam, My father was working for Agarpara Jute mills - kolkata, And he worked for near about 35-40 year year in same organization . And he was passed away in Sep 2014. Then we went to kolkata to claim the Pf, Pension, EDLI and gratuity. The employer did not give us the any receipt for receiving the our claim form. Then i made the RTI to pf office about unexpected delay . Then Pf office release our all money like PF, Monthly pension and EDLI except the gratuity. Then we were waiting since long time and we did not get back from the company , then we made the complain to labour commissioner at Barackpore - WB in form N. Then Labour commissioner invited us . Then the company advocate said , he (my father) was not our employee then we ask if he was not your employee then how we got the money of PF, pension , and EDLI. The labour commissioner was asking for appointment latter , but we do not have the appointment letter . We do not think 35-40 year back , the company used to give the appointment letter . We have RTI information documents(RTI inform he was employee ), We have salary slip, We have documents for ESIC where mention it my father name showing employer name . May i ask your help and how can we claim this money. We are looking to hire the advocate for kolkata region also . How much expected cost will come for hiring the advocate .And how many year will take to settle the cash. Thanks and regards D K Pandey new Delhi