Not received Full & Final Settlement and Relieving letter

Hi, I worked in a company based in Chennai in 2021. I resigned and relived from the company in November 2021. It's been more than 6 months, and neither I received my Full and final settlement, nor relieving letter. I took multiple follow up with HR and my manager, however, I'm not receiving any concrete response on the timeline by when I'll receive the amount. When I joined that company, they sent me to London for a month and before that asked me to sign a bond which states that, after coming back to India I can't leave that company for a year and If I violate it, I have to total costs incurred towards the trip to London, apart from one year’s gross salary. My colleague and I signed that bond on the same day. He left the company 4 months after coming back to India and didn't have to pay anything. He also received FnF after 5 months of relieving and relieving letter after 15 days of his last working day. Now when I'm following up with the higher management, they are asking me to pay the full amount which comes around more than 15 lacs. I need advice on this how should I proceed further with this.