If you are on Airtel 256 Kbps post FUP, just call them and ask the CC to transfer the line to Cancellation department. Then tell the Cancellation person that since you want 512 Kbps as a minimum speed post FUP which is not available on your plans, you wish to cancel. Insist for cancellation and they will offer you a 512 Kbps post FUP plan. Airtel actually provides 512 Kbps post FUP but not to all customers but only to those customers who go for cancellation by getting fed up from their low speeds of 256 Kpbs. This way they save by not providing to all customers in general.
well regulations would eventually be implemented and 512k would become the minimum speeds on broadband branded plans. i guess airtel is just preparing for that eventuality by offering it as minimum on their high end connections.
GoI wanted to increase the minimum broadband speed to 512 Kbps but seeing the slow progress in broadband penetration and spread in the hinterlands of the country decided to keep it at 256 Kbps. They should rather have a separate policy for broadband for the metros and separate policy for broadband for Tier I, II & III cities wherein 512 Kbps can be kept for metros and 256 Kbps for Tier I, II & III.