iPhone 5S IOS 8.2 3G issue

Hi Apple,

I just travelled from UK to India and am using Airtel. 2G works but 3G is not being picked up. How do I activate 3G. I don't see any option in settings to activate 3G as well? I spoke to the network provider and they say 3G is active on my sim. I perfoI need help really bad. As 2G is super slow and I need 3G for my work. Apple please help asap. Happy to provide additional information.