Company Policy & Gratuity - 1 month short - company changed policy and made it 2 months notice period

I was working in this company (Service based Software) till yesterday and I have also served notice period of 15 days. My joining date was August 2014 and I have almost completed 4 years 11 months. I have given my notice period of 15 days on 2nd of July. However, The HR & Director told me that company has changed the company policy and Employees have to serve 2 months notice period at least. Especially, The Director of the company has said that company can change Policy any time (How can they change Policy without any notification).
The company has not notified me before my resignation via email or not given any written material for serving 2 months of notice period. I have seen my offer letter and there also they have not mention any thing about notice period. They have stopped my June 2019 salary which should have been credited on July 10 2019. Even please tell me that am i able to receive Gratuity from the company. I am falling one month short to complete my 5 years term and I have completed my notice period on month before.
What step should i take. Please advise.

Hi,
Yes employer can revise the policies from time to time as it might be mentioned in your Appointment, however it should be informed to all employees prior to effect it. As you have completed 4.11 years I would suggest you to complete the balance notice period and get relieved properly. You are very much eligible for gratuity provided if you complete 5 years of continuous service. At the time of reliving make a request for your employer for gratuity in writing and your employer is bound to clear it within 30 days from your date of relieving. Else you can take up the matter with Assistant Commissioner of Labour of your jurisdiction. Holding salary after resignation is also not right as per law.You may represent to them to release salary for your day to day expenses.