Airtel — postpaid sim and 4g dongle

I bought an airtel 4g hotspot device and post paid sim in september 2019. I paid rs. 2000 for this. They promised high speed internet with this. I asked specifically about congestion and network issues in the area where i lived. But still they promised high speed internet. My plan was 399_50gb per month datacard plan with monthly rental of rs. 399 + 18% gst. But this connection has never worked. I tried to connect for few days and only airtel page was opening. It was not even loading google home page. I was really frustrated about this cheating and losing 2000 rs. Later when i asked people i realised that many people have lost money like this.
I did not pay the bill as it has never worked for me. When i got a call from customer care i had told them to disconnect the sim. But i am still getting monthly bills for this sim that has never ever worked. I haven't even tried to connect it after the first few days in september.