Resigning from a Central Govt Organisation.

Sir, I am currently working in a statutory autonomous Central Government organisation. I completed 4 years in the organisation where the probation period was for 2 years. I have passed the probation clearance exam, the result of which was declared this month even though it was conducted in June 2022. I have got admission to one of the IIMs in April 25 2023. I submitted my resignation on 26 April 2023 requesting t be relieved on 26th May 2023 after serving one month's notice period as I was not yet confirmed in service. First, what I want to understand is whether my notice period is one month or 3 months. I asked several officers in my organisation, but no one knows the right answer. I have completed the probation period and passed the probation clearance exam as of May 2023, but no confirmation order yet received. Also, the exam result was published after i tendered my resignation. Second, even if the notice period is 3 months, can I leave the job on the given after giving 2 months salary. No reply regarding the same is yet received from the head quarters and the date of relieving which I requested in tomorrow. What steps should I take to get relieved in time so that i can join the IIM ?