Samsung Galaxy S3 — "Not registered to the network" a Samsung recurring problem

First of all I would like greenman in the Sam mobile Forum for his efforts trying to help me to solve the "not registered to the network", I still have the problem and two days ago I went to a Samsung service operator and the person there did not knew anything about firmwares or the phones itself, even more she said all the Samsung phones where defective and I should never update the phone OTA as this could burn my phone motherboard also if I use a generic battery my phone will also burn etc etc etc, one thin she said is my phone came from France but she also said the phones for America and the ones for Europe where totally different so Samsung could not service my phone at least at that authorized Samsung service center, so I took my phone and went away from that place.

There is another Samsung certified service center capable of repairing my phone but still I want to learn how to fix it and as the very last resource I would send the phone to that service center.

I would like to bother greenman again but from his posts I think he manage very well this issue, but any help would be very much appreciated.

My phone was bought in Amazon , unlocked and actually it is rooted.

Andhere is my phone info (Spanish)

S3 Info

NOMBRE DEL DISPOSITIVO GT-I9300
TIPO DE DISPOSITIVO m0
NOMBRE DEL PRODUCTO m0ub
BOOTLOADER I9300UBUGML1
VERSION DE BANDA BASE I9300UBUGMK1
VERSION DE PDA I9300UBUGML1
VERSION DE CSC I9300UWHUGMK1
CODIGO CSC ORIGINAL PCW
CODIGO CSC DE DE FIRMWARE PCW
CODIGO CSC ACTIVO PCW
PAIS DEL CSC PANAMA
ISO DEL PAIS DEL CSC PA
OPERADOR DEL MOVIL 73402
VERSION DE KERNEL 3.0.31-2320216 SE.INFRA@R0301-08 #1 32-bit
MAQUINA VIRTUAL DE JAVA DALVIK 1.6.0
VERSION DE ANDROID 4,3
NUMERO DE COMPILACION JSS15J.I9300UBUGML1
IMEI 004999010640000/01
NUMERO DE SERIE ANDROID 3230a08fec577089
NUMERO DE SERIE SAMSUNG 00000000000
PLACA smdk4x12 {32-BIT]
PLATAFORMA/CHIPSET EXYNOS4/EXYNOS4412