While such failures are not as common, we had the opportunity to see complaints from some users about it. The problem basically is related to the removal of the device configuration data. To fix just have to reconfigure data internet in our device with iOS 8.1.2.
For these just have to go to Settings> mobile Data> Mobile Data Network. Here we have to check that are configured mobile data and Internet sharing. Of course, it is also important to check that the mobile data is enabled. Once the change is advisable reset the device or put it in airplane mode for 30 seconds, for these changes to take effect.
If nothing works, it is likely that the problem is in the service provider, so you will need to call technical support from your mobile operator.