Notice Period different in Offer Letter and Service Agreement

I came to know that my Notice Period at the present company is different from Offer Letter to Service Agreement. In my Offer Letter it is mentioned my notice period as 30 days, where as the company is now saying I should serve 60 days. They are saying in Service agreement it is mentioned as 60 days. Please someone advise what should I do?

you should talk to your PRO, superior authority regarding same, showing them the terms mentioned in your offer letter. i guess that is the best thing you can do.

I think Service agreement  has more validity than offer letter.

Thank you so much for your advise.

Thank you so much for your reply.