Manager not releasing within 30days of notice and buyout request also

Hi, As per my offer letter, this is mentioned: Termination: The notice period applicable for separation from Capco’s services is 90 Days. The Company reserves the right to terminate an employee at any time without cause, however you shall be paid 90-day notice period. After the end of your probation period the Company may terminate your employment without notice or payment in lieu of notice if you engage in serious misconduct or act in manner that would justify termination without notice. This may include but is not limited to the following circumstances: (a) willful disobedience of any lawful and reasonable order; (b) guilty of any criminal offence; (c) serious or persistent breach or non-observance of any conditions of employment; (d) failure to comply with the anti-bribery policy of the Company; (e) the provision of false information during the application for your employment or thereafter; or (f) habitual negligence in your duties there is no mention about employee notice details, i got a better offer with 100% hike and joining is in 40days and they are ready to buy out also. Currently am on bench, as soon i submitted my resignation my manager pushed me to project and asking me to work 90days and not to inform my client. I cannot compramise now as the hike is 100%