Software problem with Note 4

My Samsung note 4, keeps turning off, I took it to my local repair shop who have diagnostic it with the following problem:
Phone model on the product sticker shows as SM-N910f (international version) but the actual BOOTLOADER shows SM-N910p (US version) which means originally the device is from SPRINT network US.
Device has been modified from the original state to look like a international version
Current issue- phone does not accept any of the firmwares we tried to install due to the...

Software problem with Note 4

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