Resignation not accepted

I have resigned through official email to my manager dated 7th Aug 2021 with due notice period of 30 days as per my appointment letter clause and asked to be released by 6th sep 2021. But he replied as not accepted without any reason. Again I replied on the same mail after discussion with my HR on my final decision to resign and requested to get released on or before 20th Aug 2021 as my final working day. Again he replied as rejected and not allowed but with no reason. I escalated the mail to zonal level heads of my department as well as HR highlighting the terms of resignation in my appointment letter which says 30 days notice or salary in lieu of such notice period from either party. My both proposal to serve full notice or early discharge has been denied in writing but without any reason. Now they have stopped communicating and when I called my manager he said to talk to HR and when I called HR, he says you have to serve the notice period then you will get the acknowledgement soft copy at the end, which I am not sure. Now I have to join a new company at the earliest, how should I get the acceptance of my resignation as I am not getting any written acceptance of my resignation or acknowledgement of last working day, as I need to submit it to my new employer for joining.