Airtel - Internet is not working speed idmb s

What happens to Airtel, when I purchased a new Airtel card the internet speed was good enough and now from last month it is a very unreliable internet speed what to do? The so-called 'services' of airtel are nothing but a big giant fraud that airtel company just did with me.
The internet service was good initially and now not working at all, what is this? , Just to attract buyers? , I just regret on myself to buy this service.
Please help me, solve my problem as early as possible.
Internet speed: *.* - ** mb/s ??????
(initially, it was ***mb/s)