Backdated confirmation after resignation

Sir, i am working for a reputed bank. When i took the offer it says probation of 6 months. Here my attendance , confirmation process, resignation are on the HR online portal. HR policy says that "if the employee has not received any confirmation letter from authorised HR personal then it is considered that he / she has not been confirmed in the service" Completion of my 6 months probation period was on 18th october 2016 (confirmation due date). I have tendered resignation on 26th Sep 2016 and my super boss rejected it with reason stating " i am not his reporting manager" then i mailed HR to tag me to my immediate supervisor and they have did the same. After that I have again initiated the resignation on 19th October 2016 (one day later than my confirmation due date), the HR portal has AUTO filled the notice period column as 30 days, as i am a unconfirmed employee as per HR PORTAL. still I see my HR portal that i have not been confirmed by my immediate supervisor till date (27th Oct 2016) and my immediate supervisor is very much aware of my confirmation due date by auto mailer sent from HR portal .But they are threatening me to service 90 days notice and still they claim that they can do back dated confirmation. I have screen shot of my resignation and screenshot of HR portal about my confirmation pending and all mail communication as proof. Resignation on probation is 30 days notice period and post confirmation it's 90 days..please clarify how to proceed and what is my notice period.? Any body please help me in this matter..awaiting for experts view.