Full and Final Settlement and Relieving Letter put on hold due to breach of Non Solicitation Agreeme

I was working in an IT firm which employees around <1000 people. Through this firm I was deployed to Client location where I have rendered my services for close to 9 years. However in beginning of 2021, the client has ended the contract with my firm and my firm has conveyed me that the last working day with client will be second quarter of 2021. Meanwhile I have put my resignation and served the notice period as per company policy. In july 2021 , I have joined a new organization and they have this shared services concept. Meaning , we can work for multiple clients. At the same time, my old organization got to know that I am rendering the services to the client I was associated with there by invoking non-solicitation agreement which was signed by me in May 2021. I am not providing any services to the clinet and I have informed my old organization that I am not associated with the client but even then they say that they have evidences that I am associated. The client I have worked with is not willing to give me NOC certificate since they say it is between me and the old organization.Due to this, the company has held my FFS for past 4 months which includes gratuity and also my relieving documents. Can you suggest me how can I tackle with the current situation.