DB Pune is trying to build an inventory I guess. They do not have any plans on ground to hire people. They are simply asking you to appear for interviews and confirm about your selection, only to wake up a month later for the next process, which is again an interview.
Simply because people do not want to spoil their relationship with any company, they are able to get away with such an immateurish behavior.
I am also not too sure if the HR person calling on behalf of DB is a permanent DB employee or not, so it has become very very difficult for people in Pune to trust DB HRs. I understand they cannot reveal everything to you, but there is a degree of transparency expected out of HRs, when they expect 200% of clarity on everything from us.
Total Time waste, appear only if you do not have anything else to do in life.