Airtel — harassment by collection agency

Address:

10-2-2 Flat 502A Nafees Residency, AC Guards, Hyderabad, Telangana, 500004

I am receiving number of calls from collections agency for payments on a phone which had been disconnected in march 2019. The phone number is [protected].
I paid rs 2000 on march 9th 2019 and the airtel executive who collected the money called the technical staff to disconnect my phone.
After 7 months i am getting calls to pay rs 4000.00 for the same. I spoke with customer service superviser mr randeep singh and he expressed his inability to set right the matter. I have not received any bills to my home address as i have not used the phone since march 2019. I request to resolve this issue and stop harassing me as i am suffering from renal failure.