Isaac ji is correct.
Also check the nomination form filed by your father!!
Amount is not much...if the amount were a big amount..then you had to prove that you had earned it and invested in the name of father as a joint investment! otherwise other legal heirs may place their claim!!!
There was a circular 'dated a couple of years back' from RBI (it must be there on the website still. which I had downloaded a few months back) which suggested to banks to propose a/c holders to have 'joint or survivor' mode of mandate..........
It reccomended to append 'or survivor' for almost every options of mandate....
In case if more than two people as a a/c holders... (e.g. father, mother, daughters )...it was 'joint or all survivors or survivor'
It had a very significant meaning....
Just "joint" mandate is discouraged......
Also "former/latter or survivor" or "former/latter or joint" is also dangerous...may create problems laterwards!!! if parties develop dispute, strained relations.....one party may take advantage of it!!!
if joint a/c then.... that word as "joint" should be the "first word" in the mandate......."survivor" is reccomended as the last word.
RBI circular was really informative!!