Can you share more details? Where did he pass away? If in a hospital, the hospital will issue a cause of death certificate. The hospital then sends it to the local municipal office and you can collect it from there on a specified date.
Since more than 21 days have passed now, go to the local municipal office and explain the situation, they will help you out. If necessary, do grease some palms as in this time of grief, you don’t want to fight other battles.
I’m sure, you aren’t the first one to have faced this, so don’t lose heart, there will be a way. Also, like another commentor said get 20-25 copies of the death certificate (max they can give) as in banks and other places, they ask for original copies to change the name of the nominee in the account, transfer of SIM etc.