One97 Communications — Unknown transaction

Hi pls help me somebody using my account to recharge through one 97 communications almost they used 11000/- ruppes from account as soon as my account credited, they are using it. I am help less i complained to the bank but they are unable to tell the details pls help me. Last transction done on 16th feb 2017 pos no[protected], please provide me the details those are my scholarship money. i want to know how other person using my account it was a large amount. your response will help me alot so that in future i wil make sure that it wont happen.please do need do needful. i am wiating for your reply, hoping you to resolve my issue as soon as possible.