i9195 network error

if i choose 2g: everything ok
3g or lte: network display icon is normal (full), but i can't call any phone, when i check ussd code (*101# in my country-vietnam), it show "connection problem or invalid mmi code ", sometime it show "not registered on network''
please help me.
imei and serial number is fine!

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i9195 4.4.2 unlock??

Is there an unlock available for the i9195 (uk) running 4.4.2 yet? the service menu is disabled :(

It appears that it is possible to flash to an earlier ROM then access the menu and unlock then reflash?

If this is the case, what is a sufficiently old ROM to flash back to?? (a link would be magical!!!)

Thanks

I found s4 mini i9195 with carrier locked!hlp me!

Hi guys,
days ago , I found a mini GT- i9195 s4 , I restored the phone and I put the sim , but as I imagined is blocked .
but without pin , simply does not detect the SIM , the service network is out of service.
I installed many firmware , no I detect the sim , I used "regional lock away" , " sim unlocked by spooky " , some ROM tell me IMEI " null " but I detect no sim.
I also another s4 mini identical one , I tried to change the IMEI from one to another , but I can not.
you can help me?
help me please