Airtel — not providing product purchase bill

I bought a airtel dongle before 20 june, 2017 at location emc office, bangalore. And imei [protected]. They have not shared the dongle purchase invoice till now. Every now and then they will say airtel has sent you or today they will send you.
I have dropped the email to few people :gopal. Vittal, sbm, ceo. Direct, net, 121, sanjay. [protected]@airtel.in.

I hope this time it will be resolved.
Customer name : neha chaturvedi