No u are wrong u can use your old number umder this exchange offer. U just do one thing start mnp process and wait for your no yo port in jio network.
After completion of mnp process just take ur old phone to jio shop for exchange. Now you can use your old phone no with new jio phone under exchange offer of rs 501
Ya bro may be you were right the shopkeeper and the social media people misguided me today again I visited Jio store where I got to know about this that if I want to port I've ro show phone and when it ported I've to visit again to grab my deal and exchange the phone.
