Airtel - Airtel hotspot refund

I had purchased Airtel hotspot from Airtel.in. I had paid them six months advance a rental plan that was for Rs. ****/- with a speed of ** Mbps through Paytm to their executive who came to me with the hotspot.
The speed was not even * Mbps. I complain to them for the speed but there was no resolution. So I deactivated the connection within a week of purchase of the device and asked them to refund my money. * months have passed and since they are making excuses that they have not received the payment or they will refund my money. I told them if I had not paid them how come I got their hotspot and got the service activated.