Regarding resignation not accepted

Hi. I have resigned on Feb 4th 2019 and my resignation has been accepted by my HR team and they gave me the last working date as 6th March 2019. However the Resignation is rejected by the CEO of the company. My offer letter says notice period as "ONE MONTH" of which I have already served. After tons of emails and phone calls, and meeting in person they are not ready to relieve me. Instead they are asking/ forcing me to come to work beyound my 1 month notice period. Also my salary for Feb month is on hold. I tried reaching them couple of times through email and phone call, but no response on what could be their reasons . Need your help/guidance on this. Can anyone help?