IDFC Bank — Registration problem

Hi I have an existing idfc loan account. Idfc sent me this easy buy card. I was trying to purchase the durables using it via instacred, but insta cred says the mobile number I am trying to login with is not registered with any of thier partner banks. And I have only one mobile number, which is alone registered with idfc. I wonder why they sent a card when I am not registered with them. Why did they sent this Card? To trouble us to not to buy anything or to humiliate us stating you r not registered with us . I want to use the card, my registered number says its is not registered, help me out