Airtel — harassment even after timely payment

Address:

Hyderabad, Andhra Pradesh

For past three months despite timely payment of the airtel mobile bill, i have been harassed by airtel with sms, calls asking for payment. I have shared proofs to their appellate, nodal officer who send in their apology but don't correct their system. Their contact centre accepts that their system is not efficient to track actual status!
I want airtel to ensure they stop harassing a loyal customer who settles payments every 15th of the month when the due date is 21st of the month. Also to apologize for this monthly harassment and assure this will not happen ever again. A customer should not be suffering because of poor systems and processes of airtel.