Airtel — airtel broadband (airtel black id - [protected]) closing of broad band and conversion of postpaid number to prepaid

I have been using Airtel broadband (Airtel Black ID - [protected] )
My internet is not working from last two days. It has been more than 24 hr issue has not been resolved. Even after calling customer care, three time I am not getting any possible resolution and my internet services do not get resumed. I want to close the account and have paid 586 Rs (Payment receipt number[protected] and order number[protected]) amount which has been asked by customer care team. Now they are asking me to call after some time instead of closing my account.
I want to close my broadband account and want to convert my postpaid number link of same Airtel Blank ID into prepaid number. Now, Instead of support different excuse are coming.
Further I want to highlight Airtel is not following rule of providing nodal office contact details to customer. When I trying to get nodal officer details from Airtel site by following the link. The site is taking to somewhere else where I can only get new connection. Same is case when I tried to fill grievance at Airtel site.

Please help me with closing my broad band connection closure and moving my postpaid number to prepaid number