Airtel — Post paid mobile connection permanently disconnected without notice

1) I have a post paid mobile connection for last 15 years which has been abruptly disconnected without any notice. The help desks now cites a reason of non payment of 800 Rs.

2) The disconnection done for non-payment is wrong. See the sequence of event

- I had received a invoice on 12 January 2022 and I have paid in time. All my previous invoices for last 15-16 years was on time.
- I did not receive any invoice in Feb, March and April. This is a miss from Airtel end and not my fault.
- I received the next invoice on May 12 with a deadline to pay by May 22nd. Please the attached screen-shot

3) Now the connection was deactivated before 22nd May without any further notice.

4) I have a credit limit of Rs 2000 and the remaining dues was only Rs 862. Why would you permanently disconnect when the deadline of payment is not breached and within the credit limit.

How can I reactivate the number?