Company not accepting my resignation and changing the contract

Hi, Sir . This was . i need a suggestion to approach about my problem .I was working on my startup software company since 5 years . i got good opportunity in good MNC company . as per the company rules one month is notice period and first one year from the joining is the contract period and we are working on our company self project from 3.5 years . after getting the opportunity i was given resignation letter to company via mail and given 1 month notice period . but the management is not accepted and they are not giving proper reason for not acceptance. I do't want to for this organization anymore . when i joined in this company i got offer letter with 1 year is contract period and one month is notice period now they are changing words and saying other words . Please suggest me how to go through labor law . please do't publish this in any article an contact with me through email not by my contact . i am requesting Thanks.