Bank Branch Manager misusing the power

Hi All I am a lady. Two years before I lost my husband. I am getting his pension after his death. My son is having a home loan on his name. I am not a part of that home or I have not even signed any legal documents for that home or home loan and I am not an nominee. Once my son was short of money and did not paid the loan amount for 3 months. so I asked branch manager to deduct it from my account and I gave a written application for the same. After that my son started paying it on time. But whenever my son fails to give loan amount on time branch manager started deducting the amount from my account without informing or without permission. Even my son was not informed. When asked to the branch manager we were informed that as your son fails to pay it we will deduct it from your account. But I have not signed any legal documents for loan or I am not any part of his property. I just helped my son for one time and it was clearly mentioned in the application. And I have phone regards and proofs too. Why I should be hold responsible for non payment of loan when I have nothing to do with it. I just want to file a case against the branch manager for rude behaviour and misusing of his power and fraud. Please help me out