Relieving letter from current bank

Currently I am working in a govt bank which I joined 6 months back. Before i joined my current bank, I had applied for examination for another better govt bank. In due course I gave the Prelims and Mains rounds the progress of which i kept sharing with my branch manager, and got selected for the next Interview round. The call letter mentioned i needed an NOC, No Objection Certificate. I googled the format and intimidated my branch manager regarding the requirement of the NOC. He didn't forward it anywhere and wrote the noc for me and undersigned the document for me stating that I would be released in case of selection. When I appeared for the interview, everything went fine, they kept the noc but said if you are selected, the next time you come, bring proper relieving letter from concerned authority. Now I got selected, I am wanting to resign, but my authority is asking me to hide the fact that I got NOC from BM and take resignation. I want it to be proper, but they are trying to hide the noc of BM because he didn't forward it to concerned authorities, else not helping me. I know am right, because I duefully intimidated and requested my Reporting Authority for NOC, and received an NOC from him which he gave me, it still remains an NOC only. Please now help me and guide me in the proper route.