This is a strategy 100% certainly designed to make it hard for you to get another job. Just leave. What do you have to lose - your job? It may impact your referees but explain that to the next employer, they should understand that you are the victim of a predatory employer.
Its not just my employer. All the biggies in India have changed their policy at nearly the same time.
Did you sign and agree to the increase? What was it before? What were the terms of your original service agreement?
The Increase in Notice period was coupled with an compensation review given a few months back. They Informed us that they were changing the policy, No signatures at that time.. But I guess the documents signed during joining the company would contain clauses to justify the interim policy changes.