airtel offering waiver on surrendering tata docmo dongle but 4g sim not performing & in this case not returning dongle or equivalent back

After 3 days only I wanted to close my 4g data sim 7760973223 due to performance issue & want back my Tata Docomo dongle or equivalent but company refuses to give it.
Complaint 1: Airtel is offering 250* 9 month waiver against deposition of any working dongle. It is a big fix because if you discontinue airtel service later due to performance issue then they are neither returning dongle nor any money or equivalent.
Complaint 2: Why they are selling 4G data sim at 100/- cost & also converting in free existing voice sim to 4g sims. Only for money & filling dual sim second slot.
Complaint 3: Not answering mails & executives refusing to help on call. Can be checked from call records