Issue with notice period- HR is asking to serve more notice perio

Hi Sir, I am facing issues with my current employer [XXXX Pvt Limited], I received an appointment letter for serving 30 days notice period if i am in Probation period, And on my offer letter its clearly mentioned that my probation Period is till Oct 2016. Now my employer saying that policy has been updated and revised notice period is 60 Days, but no communication or written letter is sent to me regarding this and no update has been shared from employer. also i have not signed on any communication. Now i got an offer from another company with good profile hence i have submitted the resignation to Hr marking my manger and mentioned 30 days notice period with my relieving date, but my employer says that you need to serve 60 days notice period. ( 60 days notice period is applicable only for employees who are confirmed employees but i am in probation period till OCT- 2016) i have submitted the resignation on 2nd Aug 2016 but still its not accepted from hr so please let me know if there any time to apporve the resignation like 3 days ? I have checked with my employer about notice period Buyout option but my employer says that the option is not available, but it’s clearly mentioned in offer letter that salary in lieu option is available. Please advise me what I should do about this ?