Not giving NOC to join SBI PO even due to departmental proceeding .

I am serving as SBI clerk. I resigned from the bank on nov 2019 and asked for NOC to join fresh SBI PO . My HRM informed me that one departmental proceeding case is pending against me and hence my resignation could not be accepted. Subsequently all the enquiry process was completed till july 2020. However I was charged the punishment which states as follows :"reduction to a lower stage in time scale of pay by one stage for a period of one year." the concerned persons told me that it won't affect the resignation. It will only affect the amount of PL encashment. I had requested for extension of joining twice and now i have been allowed to join with next batch SBI I once again requested my HRM to proceed with my resignation request. However, they have still not relieved me. Gm telling that they will not allow me to join SBI PO. What is the law .why they can play with my career . Please suggest me . What to do ?