You have made the mistake which majority of the innocent, ill informed, hapless, gullible customers make, and later suffer harassment.
From various publications, threads at LCI too, and experience of known ones it is construed that this company Airtel is notorious for fleecing its customers.
The question arises should a customer cancel/close the connection in the manner you have done? The answer seems to be: NO.
The customer should instruct the company (any company for that matter) in writing under proper acknowledgment with seal and signature of the competent official of the company.
In your case you have posted that you are getting e-bills implying you have registered your email id with the company. Thus you could have sent email for disconnection/cancellation of connection issued in your name.
Although you have made the full payment the collection has not updated his company the receipt of the payment as FNF payment. The collection executive does not have such power. He has collected his commission and is happy.
You may post your facts in writing to MD, Company Secretary, Chairman (collect contact details and address from website of the company) and ask these good offices to intervene and issue you the FNF payment receipt and a certificate of cancellation of connection.
You may also post to Nodal Officer/Appellate authority.
You may also apply your resources and approach the collection executive ( before he vanishes) and local BM and obtain the requisite docs in your favor.
Moreover the company does not close the connection by payment on prorated payment. It shall close on payment for Billing period.
It is also noted that:
--If the customer visits the company’s office with a letter to close the connection the company does not agree to acknowledge the receipt of the letter by affixing seal, signature and date on the copy of the letter. It simply gives transaction number verbally.
Later the billing does not stop.
--The company officials in retention, sales etc do not post proper advice and rather mark the connection to collection/recovery.
It is a malpractice but it is like this.
In one case the customer after making full payment moved to another location in another state but continued to be harassed by so called advocates.
The customer later arranged a crowd of well wishers and blasted the local BM and the BMK was made to resolve the matter on the spot and issue a communication that connection is cancelled and nothing is due to customer.