Reg: TDS 20 deducted

Hi,
actually i made Fixed deposit 5years on my sister (minor) name in a bank. I have submitted PAN of my father (Gaurdian).
since last 5years bank people deducted 20% TDS on interest amount and paid to Govt.due to not available of pan of minor girl.
They not informed us reg deduction.
They failed to accept form 15G also..
Now almost upto 50k TDS blocked with govt.
Now i applied PAN of my sister and it is available now..

how can i claim the refund of TDS?

do I need to rectify Bank TDS returns which are previously filed with PAN??

Pls help its urgent...