Airtel — Broadband bill generating even when after disconnection

Airtel is continuously calling me to pay the bill even when I am not using their connection for past 1 month.
I should ideally pay for just one month but their bill has additional amount of one extra month even when they disconnected my internet in the beginning of February.
When i started this connection they took 3 months charge from me in beginning. So how is it even postpaid
Xstream fiber number - [protected]
My registered number - [protected]
email - [protected]@gmail.com
Name- Deepali Saxena