Airtel — bill amount issue

I had converted my airtel postpaid account to prepaid by clearing all the due as per my airtel app. Now after that i am getting message for postpaid bill amount. I am not able to find the details of this amount neither it is showing in the app. Tried contacting customer care but all fail. Myairtel app customer support also does not redirect me properly. I am not sure whom should i contact. I am not going to pay any over burden charges due to this mesh. Airtel should work on customer complaint and services sections.