Airtel — not deactivating my airtel number...

Address:

Mumbai City, Maharashtra, 490607

I had and airtel data card number last year in 2017... After using it for 5 months... I requested them to deactivate this number.. But still this people didn't do it... N kept on sending me bills... Later again... After 2months airtel person calls me to pay bills... I again requested to deactivate this number... So they told me to pay the bill we will deactivate immediately but it will take 24hrs n u will receive a mail regarding that...
N i waited waited... But didn't received anything.. N later i even forgot about it. Now suddenly after 7-8 months they have sending a legal notice that i haven't paid the bill of 13000/- for the same number which i'm not using it n this airtel person have not even deactivated this number...
They are here to fool us and extorting money from us...