Resignation Dilemma: Manager Agreed to Short Notice, Now Backtracking – Is This Fair?

Hi, I resigned from the organization after a discussion with the reporting manager. During our conversation, I mentioned that I would only be able to serve a 15-day notice period instead of the standard 2 months. He agreed to this at the time and confirmed via email.
Now, he is saying something different. Is this correct? Please confirm.

Deepak,

An email communication satisfies legal requirements. So, feel happy about it! The only matter you should confirm in your HR Manual is that your line manager was authorized to approve such waivers.

Best wishes,
Rajesh