Idea netsetter with 2g sim
Very poor downloading speed

I am devarajan from villupuram. i have recharged my idea netsetter on 11.9.2011 with rupeess 599 and it is noticed that the validity is for 75 days unlimited download. the speed of download is normal upto 04.10.2011 and from 05.10.2011 the download speed is less than 40 (forty) kbps and this is giving much mental torture to me. so far i used 1.6gb only. when i try to ask about this they simply tell call *147#. but in that fecility there is no proper answer for my problem. so i request why the idea announced 75days unlimited download with rupees 599?