I am facing the same problem for a year now. I have changed by sim card twice asking for Diamond OMH card. Number remained the same. 
I have a Samsung Y i509 CDMA handset.  
However if I change the sim with my colleague's sim (checked with 3 different simcards) then internet works. 
I also have a monthly 1GB plan for Rs 125/- that I am paying but cannot use. 
I have made upteenth visits to Reliance world stores but they are clueless. 
Quality of Customer service is pathetic. 
What are my options......? 
Any solution....? appreciate speedy resolution if possible.