Default Problem with Mobile Signal

Dear ever body. I'm from Vietnam. I had a problem with my mobile signal! I tried my best, but i could not solve my problem, inculded: Recovery Cook Room, and Stock Rom and Firmware.
My problem is auto change mobile network with 2G/3G VN Mobifone. It didn't work. if i selected GMS (2G), it could recognize network, but when I selected auto network or 3G network, It didn't work.
MY HTC ONE M7 is International Asian HTC.
Sorry about knowledge English (bad) and thanks a lot for your helping.
Waiting for early response from you.
again, thanks a lot.