Succession certificate is the laid down legal procedure for a claim on deceased property, and when the death was intimated and recorded, unless the claim is settled every legal heir, as co-sharers are trustees and enjoy possession and enjoyment. As already a petition was filed for SC, contact the local advocate that is handling the issue, bring the fact to the attention of the court.
The presumption is that the amount was with a bank, and the bank has settled the nomination, and you might have not issued and made the bank as a party in SC petition. Unless you make a claim, the bank may not be coming to know of your rights. In absence of notice, the bank is proper in settling the claim and finally, the party who has withdrawn the amount should account for the legal heirs (other co-sharers)