Can an employer revoke reliving date after confirming in writing

Hi!
I had a discussion regarding my reliving with my reporting manager. During the discussion we believed that my notice is 2months. However, I requested for an early release to which my reporting manager said, I will get back to you after discussing it with HR and HOD. Upon follow up the manager responded back with a definite date on email.
Now I received another email from the manager stating that as per the discussion with HR notice period is 3months so now technically its 1 more month and said I didn't check with HR before giving you the relieving confirmation email.
Based on the earlier reliving date confirmed by my manager I have already informed my joining date to the new employer.
Pls suggest how do I tackle this situation now.

Hi Friend,
Ignore everything and just refer to your appointment letter. The duration of notice period mentioned there is the one you need to follow.
HR can relieve you before with mutual consent however cannot force you to extend unless it is a request duly accepted by you. Anything apart which forces you is a breach of indian contract act 1872 and also an action against the provisions of bonded labour system abolition act 1976

Thank you Harpreet Walia for your revert.
So I understand that the Manager can change the relieving date unless its within the defined notice period as per the appointment letter.

"we believed that my notice is 2months."
What was written in appointment letter?
How can "we believed" instead of "we know"
Your manager was also negligent in confirming your departure date w/o checking from HR also.Now I suggest you speak to earlier employer and request early releif since you are committed to new employer.
Offer to pay for notice period if insisted upon.
The problem has arisen because basic information was not known correctly as to duration of notice period.

Yes Nathrao... Despite of my reporting manager stating that I will get back to you after discussing it with HOD and HR the due diligence was not done from the Manager's side and instead of accepting the mistake the Manager is covering up by saying You have to give full 90 notice. So why is it employees fault if the manager is negligent. Can I stick to the previous relieving date sent by Manager and take this matter to HR to reslove this now... Or there is no point arguing? I have already updated by new employer on my joining date based on the previous confirmation email. Plz suggest

Organisations seldom agree to mistakes.
You need to navigate this issue carefully in friendly manner keeping current and ex employer in loop.