Need to Hit refresh Multiple times

Hey,
I was previously on night unlimited plan at 2mbps but since they stopped that plan .. i got my bb disconnected. I started using it again last month and i have now got myself the 675 unlimited combo plan.. but now i am having problems. Ok i understand that the speed has been reduced to 512 kbps... but now when i open some sites .. or click any random links, my browser (both chrome or firefox) will display "not connected to internet" immediately.. within 2 to 3 milliseconds... i.e. without any delay. I hit refresh but nothing happens.. i have to hit refresh multiple times for it to work..
it does not happen on all websites.. happens randomly.. not on any particular websites... and i have already switched my dns servers to googles dns in my router.. but nothing has resolved... any solutions ?

are you getting anything at the left bottom of the screen like 'waiting for 203.94.243.30'

no.. as i said the "not connected to internet" page comes up instantaneously.. it is not like it is waiting..

try pinging to 8.8.8.8 for a while and see if there are any loses or it could be related to some specific sites only.

Meanwhile clear your dns cache ipconfig/flushdns and also check if google dns are properly setup ipconfig/all