Full signal don't make calls

Hi, I have an annoying problem. My phone is attached to Telefonica Movistar from Mexico. The problem is that sometimes the signal have full strenght but I can't make calls, the persons that call me got voice mail, no Internet data. When the problem is happening, the 3G icon dissapears, for this reason I know that there is a problem with my phone and I need to reset cellular connection.

The solution that I had found is to reset the cellular connection by going to airplaine mode, hold for some seconds and back by turning off the airplane mode. The signal recovers again.

The problem happends most of the times when it is charging, but also many times when the phone is in normal state.

I also tried to configure as a new phone by reseting all the setting and factory default parameters, no luck.

The carrier changed me the SIM card, no luck.

Reset network settings, no luck.

Any ideas?

Thanks!

Elier.