Pessonal
Less interest paid for TDR

My grand father invested Rs.20, 000 and 4, 000 in SBI TDR in 1975 for 5 years when he alive. He take interest monthely in cash till he live dt.04.07.1979. He also done a registered will in favour of my father. we don't know about TDR till March, 09. In March when my father claim for the amount then SBI Industrial State Branch, Kanpur give us simple interest near about 67, 000 total. Is it legal? If not then Plz help me.