Airtel — bills after disconnection

Address:

5A,annamalai avenue 1st main road, jeswanth nagar, mogappair west, chennai- 600037, Chennai, Tamil Nadu, 600037

Dear sir/madam,
We are residing in mogappair, chennai where we subscribed to postpaid scheme in airtel for landline and broadband services. We got the connection disconected voluntarily by airtel since september 2018, we paid the bill till november 2018 for not even receiving the connection. We applied for cancellation march 2019 and we were told it woud take 30 days. Unfortunately they hadn't cancelled it and we have an unpaid bill till may 2019 because we kept receiving bills monthly.
Please help us to resolve the issue. We would be highly obliged by your help.