Airtel — incorrect billing plan, bad service and speed

I had subscribed to Airtel USB modem - Data Card. there i was given 1GB/month for Rs 599. i was assured a speed of around 240Kb/s. i hardly get speed of 100kb/s. after i got my bill, i was shocked to see.the bill was huge. this is because, ther is a minimum usage of 1MB every time i login/connect.meaning that even if i connect, but don't use, it will be considered 1MB, and if i use more than 1 mb, the count will be considered rounded upto the next level, meaning that if i use 1500KB, it will be taken as 2mb, if i use 10.5mb, it will be taken as 11mb, if i use 9kb, it will be taken as 1mb.
i was NEVER informed about this sort of billing plan.
moreover, one can know about his/her account usage only after he/she gets the bill.