Not signed new notice period policy Am I liable to follow it

At the time of my joining with my employer and as per the appointment letter the terms of resignation were to be adhered as per the notice pay policy. there is no notice period duration mentioned but as per the HR, It was 24 hrs on probation and 30 days on confirmation. Now I have completed my probation of 12 months got my confirmation and almost going to finish my third year. Last year an email from the CPO came "Subject: Change in company probation policy", stating that the notice period of all the employee of grade level AM and above has been changed to 3 months with effect from 1 Jan 2016.Now I have put down my paper's with two months advance intimation to the concerned HR. My Questions are as follow: 1. I have not signed any agreement with the employer after the change in the notice period, Is it still applicable to adhere to the new notice period? 2. My appointment letter say's I have to adhere to notice pay policy and the email say's Probation policy are both the same?