3G not working on my iPhone 5
Hey guys, I live in Brazil and I recently bought my unlocked iPhone 5 in Miami. When I got it, I updated it to iOS 6.1.4. My 3G is not working, even when the 3G symbol appears. If the 3G is enabled, I don't have connection with the EDGE network either. If I disable the 3G, sometime the EDGE works, but only sometimes. I'm quite sure the problem isn't with my carrier, because I went to the store to complain and they tested the SIM card on their iPhone 5, and it worked as it should. I'm also sure the problem isn't with my network card, because the WiFi works properly on my iPhone 5. So, is this happening to any of you? Is the problem with the iOS?
iPhone 5, iOS 6.1.4