Recruiter not mentioning the grounds for cancelling candidature

I qualified ibps specialist officer-marketing officer exam in april 2016. And was alloted union bank of india. I got provisional offer from mumbai central office at my residential adress in unnao(near lucknow) and was directed to go to union bank of india fgmo in varanasi for document verification. During document verification the officer was not satisfied with my mba degree specialisation so he said he will be forwarding my case to mumbai head office and will tell about their decision after 2 days (15 may 2017). But till now they have not replied my in written but orally they are saying that my candidature is cancelled and also they are not telling on what grounds they are cancelling my candidature. What should i do now? I have been communicating with them continously but they dont reply. Should i file a case ? Where should i file case ? In lucknow or in varanasi