My appointment letter states that my notice period is 30 days but company asking for 90 days.

My appointment letter states that my notice period is 30 days but my company is imposing 90 days by stating some internal policy I was never aware of. What should I do? "Upon confirmation of your service with the Company, you may resign the services of your employment with the Company any time during regular employment by giving not less than 30 days written notice or pay 30 days Notice pay in lieu of notice period.(Notice Pay Recovery from employee would be done along with applicable GST). However, persons in responsible posts or persons having undergone specialized training may be directed to serve the notice period and in such cases, even where any leave balance exists, the person shall be liable to serve the notice period as applicable. (Notice Pay in the Letter of Appointment would mean Basic plus any allowances (Gross Salary) that are paid on a monthly basis to an employee) As part of the exit formalities, you may be required to sign and submit such other documents, as may be decided by the Company from time to time and in the format as prescribed by the Company."