Bank charged higher interest rate than agreed rate -Personal Loan

Dear Sir, I have taken a personal loan from a private bank 4 months back. I received my repayment schedule (soft copy) and the agreement copy, repayment schedule (by post) just a month back. After reviewing the documents I found that instead of 12% interest rate (as per the agreement) they have charged 12.15% (applied). I wrote to customer care and relationship manager regarding this. I did not get a proper reply. So I have escalated this to 'Grievance Redressal Officer' of the bank. I got a reply saying that the interest rate is calculated basis 360 days which is not in the agreement copy. In the agreement copy that I have signed had 'the interest rate is "taking basis of 365 days in year/366 days for a leap year". Now, replied back by attached the agreement copy scanned document. If I do not get a proper reply from this level and next level officer I'm planning to go to 'Banking Ombudsman'. In the mean time, I would like to get opinion from law experts what if I do not get justice here and what are the legal steps can I take against this bank for this kind of practice. I hope my question is clear and I await your valuable reply. Thanks in advance!