Employer asking to pay bond amount in lieu of FFS to release Relieving letter

I have got the resignation acceptance letter but experience letter/service certificate is not released by them.

Sir will you please tell me what if they don't release service certificate after sending them a legal notice. What options left after that for me.

If legal notice doesnt work,then legal action will have to be intitiated.

sir i received resignation acceptance letter stating 'your resignation dated 8 Jan,2020 is accepted and you will be released from the services of the company on or before 3 Apr,2020 and your service certificate will be issued after F&F and payment of dues if any'. Now, my question is "is this letter is sufficient for my future employment?"

Dear Sir, please tell if above stated letter is suffice for the relieving letter, and i got this resignation acceptance letter after my last working day when all "No dues" were cleared. My last working day was 3rd April,2020 and i received this letter on 12 April,2020. Also i have a mail from them stating "your no dues formalities are completed".