BSNL sim SMS outgoing error in iPhone 15 Plus. Imessage is not working with BSNL Physical SIM

The problem of Sending SMS (When you are receiving SMS and Making to and fro calls) is resolved by following the steps as mentioned

1. Changing the BSNL Network to 3G, 2G, so that Network Selection will give BSNL MOBILE.
2. BSNL mobile number for sufficient SMS pack
3. Now Dial the USSD code **5005*7672*+91message center number#).
4. After entering the above USSD code simply click on DIAL the number. The iphone will take that USSD code and no response will be given.
5. After the above step go to SMS Imessage app and send SMS from your BSNL number to your BSNL number itself.

Contacted the BSNL. They are suggesting to check SMSC Number.