Fnf settlement

Hello All. I would like to share an incident with all of you. I was working with a firm for good 5 months and during my service period, I was asked to leave the organization as they got the replacement of mine. I left the company 16 days prior to my service period gets completed. I was been clearly told that they will waive off the monetary notice period which I didn't serve because of them. now after 50 days, they shared the fnf statement and they have deducted 16 days amount from the total as not being served the notice period completely. So, I got in a conversation with them and the accounts manager got the approval and said he will revise the fnf statement and will share soon. now after 10 days, I got an email from Head of HR that they wont as that is against their policy. I need help how to tackle this situation. Regards, Ashwani