Why am I unable to use 3g, mobile data working on 2g, when I have a active 3g data plan?

[AC Question]

unable to use 3g, mobile data working on 2g, i have a active 3g data plan

I have a sony Xperia t2 ultra which is upgraded to lollipop, my network data is working on 2g (showing 'E') not in 3g. I have already installed the internet settings and have a active 3g data plan. There was no problem in my old samsung galaxy ace which was gingerbread. Do I have to do any sort of settings???Please help to fix problem.

 

[Rukbat]

Bring the phone to the carrier. You may have no 3G signal where you are, 3G service may be down for a while, the phone may be defective, the SIM may be defective (they should replace that for free) - many things you might be able to fix, many things you can't fix. They can fix them all.