Advise on migrating to 256kbps unlimited


i'm currently on Airtel 64kbps Unlimited connexion (top-up plan) 600/month (CHENNAI)
I'd love to migrate to the 256kbps plan (UL till Aug 31..then 1gb cap)
( )
and then after aug 31 would want to come back to this plan..
but recently i heard.. Airtel in Chennai have stopped (or discontinued..) this top - up plan so .. i'm pondering...
heard 128kbps Unlimited costs 997/month.. and i can't afford that..
Any suggestions?any other alternatives? any one know if this plan is discontinued in Chennai ??
Any Unlimited night packages in Airtel Chennai?
and lastly, why the 256kbps offer ain't in the official website??