Psu Bank not accepting Resignation

I am a Chief Manager working in a Psu bank since last 10 years. I had submitted my resignation in October 2022 with 1 month notice period and was going to pay for the balance period of 2 months. Bank rejected my resignation on the grounds that staff accountability investigation is going on in 3 NPA accounts which slipped in August 2022 in a Branch where earlier I was posted. On the day of resignation I was not holding any explanation letter for these accounts. In January 2023 i received explanation letter for 1 of the accounts, I replied to it and I received final closure letter for the same in June 2023. I once again submitted my resignation in June 2023, however to my shock it got rejected once again. I was told that investigation is still pending in remaining 2 accounts. As per Bank guidelines Staff accountability investigation is to be completed within 6 months from the date of NPA but here bank has taken almost 1 year and still there is no conclusion. I am not holding any explanation letter in my hand right now for these 2 accounts I already lost one job offer due to this delay. I am totally frustrated and mentally stressed. I have already sent an email to the Management expressing my frustration over this matter but no reply for the same. Kindly guide what options do I have.