My resignation accepted but co. not ready to relieve me

Sir, I am Working in MNC and I resign my job on 12.10.2014 and I intimate the company that my last working day in co.will be 27.10.2014 and I would also like to inform you that at the time of my joining in company they give me letter of appointment in which they have written the notice priod for leaving the co. would be 3 months notice or 3 months pay.now when iam resigning my job they accept my resign but not ready to relieve me till my replacement person should be appointed.and they are not give me a copy of acceptance of my resignation. Regards. I.J.SINGH So please advice me what legal action I have to be taken if they are not relieve me.