First get copy of the revised policy of the current employer reducing the notice period to 30 days and check if it is addressed to all employees, or selected employees, or it is a circular etc. If it is circulated by email and your official email is mentioned in the address bar then it is applicable to you.
The contention of your manager, and Hr executive is false and they do not frame any policy. They simply want to deny the benefit of new policy to you.
Obtain offer letter on proper letter head of the company preferably signed by Head-HR of propective employer, with date of joining, package offered with detail of salary, descripttion of job offerred, designation, location, and a confirmation whether you have to sign a service agreement/bond or not etc....Submit a written communication that you shall be in a poistion to submit copy of resignation, POD only and can submit work experience/service certificate, relieving certificate, acceptance of resignation if and only if and as and when received by you from your currrent employer.
Then only you may submit notice of resignation with effective date of resignation clearly mentioned in it , addressed to your appointing authority, MD, Head-HR, and mention to whom you should submit company property, and handover the charge.