BSNL — difference between two 2g sims

Address:

Mokokchung, Nagaland

I have two 2g sim in the same house bought at the same time and have been using internet. The biggest difference in the sim are the speed. In one no. i receive 17-20 KB/s
but in the other sim the speed the speed never goes below 100KB/s. i tried to take help from customer care :-the reply was "depend on the luck"