Bharti Airtel — poor network and internet speed

Address:	Chennai, Tamil Nadu, 600037
Website:	Any website

I have ported to airtel from vodafone expecting good network coverage, after poring 1st couple of months it went well but now i am not even able to browse, it's a postpaid plan and i have 100 gb data left which i am not able to use due to their crappy network. I complaint to airtel and they claimed that the issue will get resolved within a month but its 3 months now, i have never missed to pay the due amount but no idea why airtel is cheating me.