Write a letter to mobile company for old sim card has lost that`s why issue me a new sim card.
You don't have to make any letter that you have lost the sim card you just need to go to the any branch that is near on your area and tell them that the sim card was already lost.
For the requirements:
2. photo id proof
Regarding on the services that in currently on the old sim card that was lost, it will still remain since it was just only a replacement.
What good feature also is you can ask for a duplicate of sim card and blocking of the sim that was lost but there will be a corresponding charges which is Rs.25 to get a duplicate SIM card and no payment for blocking of old sim card.
for more inquiries you may ask also their customer support.
You can reach them with this number: 111