Since you have mentioned that HR collected copies of mark sheets and payslips, I assume you are working elsewhere. I suggest you wait for some time. Since it's a bank job, they will certainly conduct a background check before hiring. They need to verify your address, mark sheets, past experience, and all this consumes a lot of time. Even if we assume that all procedures are completed and the background verification is cleared, it can still take some more time.
Let's say they have selected 100 people to be deployed in 10 new branches, and if the approval for these branches gets delayed, then naturally positions will be on hold. These are just assumptions; there could be some other reasons too. My suggestion is to wait. Don't quit your present job; keep trying for other jobs as well since this HDFC opportunity is getting delayed.