Company Notice period increased from 30 days to 90 days.

Hello All, I have 1.5 Year of experience in my company. I got one better opportunity in another company and I have to join there within 1 month, but as per my current company, I have to serve 3 months of the notice period or three months of Salary in lieu of notice which was verbal by our company manager. I have already given one month of notice period to my manager and told them that I will not pay the remaining two months of salary in lieu of notice, but HR told me that they will releive me once they get confirmation from my manager and he is not ready to releive me. I don't have time to serve even two months and I need experience letter and surrender copy of my airport entry pass from this company. Please let me know whether I have a legal ground to send them to notice. Because in the offer letter it was also written that "they can accept or deny the payment in the lieu of notice period, depending on the criticality of the assignment/ work as deemed fit."