I recently changed carrier for my phone i got 400MB of monthly internet to use,however there is always a roaming symbol (Triangle) on the device.And even tho the roam is disable i still cannot use 3G to access internet
You answered your question yourself. The icon is telling you that you're using a roaming connection for whatever reason. But you didn't allow data roaming.
That's something I certainly can't tell you. But the image clearly shows a roaming connection while having data on roaming switched off. So there's no wonder you're unable to connect to the internet.