You can use SMS code, BSNL My APP or bsnl portal
How to check the validity of extension Vouchers in your circle
Send PV to 53733 or 123. Then you will receive a message with the list of available prepaid plans.
1. Validity Extension through SMS using your main balance.
Send PV<amount> to 53733 or 123. Ex: PV37 to 53733 for per min plan, PV36 to 53733 for per sec. plan
2. By Automatic Extension Of Validity
Automatic Extension of some Plans., Validity will be renewed automatically on the 2nd day after the expiry of validity period, on the availability of sufficient balance in the customer’s account. Customer will be intimated by SMS.
3. By Coupon Recharge/Electronic recharge
>Go to your nearest bsnl Customer service center/Retailer shop. ask for the extension of the validity of your plan.
4. Through online Bsnl Portal
>Validity extension through online is the best and easiest method recommended
> you can do it with your debit card, credit card or net banking