iPhone 6 Plus 3G cellular data not working

I am using iPhone 6 plus running on iOS 8.4, bought it in USA (factory unlocked). Recently arrived China for short stay, bought a new sim card (China Unicom). Initially internet was working find but out of a sudden, with no apparent course the cellular data stopped working. The ON/OFF switch works just fine but whenever i switch on Cellular data, it doesn't show the 3G logo at top of screen. I travelled fairly often but this is the first time I'm experiencing this. I tried resetting the phone/network settings and even restored a previous backup but didn't work. Is anyone else experiencing this and please to you have any suggestion?

With appreciate.