As per the PPF rules 2019, in the event of the account holder's death, the account has to be closed, and the nominee or the legal heir is not allowed to continue the account. The balance in the account of the deceased account holder earns interest until the end of the month before the balance is paid to the nominee/ legal heir. So you cannot continue the account after the death of your mother. As per the government saving promotion rules 2018, for an account which has matured but not closed, the eligible balance in the account earns interest at the rate applicable to the Post Office Savings Account till the closure of the account. Since you have not closed the account, which matured on the date of death of your mother, the bank may reverse the interest already credited and pay you interest on the rates applicable to the post office saving bank account.