Originally Posted by
Hannan Ashraf 2: The country of origin of the phone on the box is Vietnam.
3: I live in Pakistan and I flashed it to original 4.4.2 version released for Samsung Galaxy Grand 2 for Pakistan.
Reflash it, using the firmware for Vietnam. The phone doesn't care where it is, it cares what firmware it was built to use. (I assume you mean that the country it was built to be sold in is Vietnam. The country it was built in is irrelevant. China builds phones for use in the US, but if you flash a Chinese ROM to them, they stop working.)