Do i need power of attorney (bank)

Yes. You can have POA. do the work on behalf of your sister. Why POA is required for this simple rectification ? Online also she can submit her grievance to the higher authorities in the bank.  or www.bankingombudsman.rbi.org.in

Yes, you can represent your sister by obtaining a Power of Attorney (PoA), which will legally authorize you to act on her behalf in dealing with the bank regarding the interest issue. The PoA should clearly mention the details of her account, the specific authority being granted to you, and the purpose of handling this matter with the bank. To make it valid, your sister needs to sign it, and it should be attested by a notary public. It’s a good idea to consult a civil attorney or use a reliable PoA template to ensure everything is properly drafted and legally compliant.