Airtel - False service promise

I am getting a consistent call from Airtel on upgrading my broadband plan to ***mbps with change of modem, but while installing this modem last year with the plan of ****, I was promised ***mbps. This time when I asked them to give on mail the benefits of this change which they refused and hardly I have seen a mail detailing all the features and of my plan ever shared with me. Request all consumers to be cautious, and request airtel to share the reason why they are charging me for a technology change which they promised they have while selling the plan to me. Request airtel to reimburse all consumers whom they promised better data speed but did not deliver. If someone can help me resolve this problem is a better way I will be thankful?