Which Version of M8 I Am Using?

[AC Question]

I need a Little help regarding identifying my version of M8

I have looked up the imie number on IMIE Data website and found that its a AT&T US Unlocked Phone.

Now when i try to flash the latest firmware for AT&T through RUU file it gets stuck at sending file stage 1/6 .... ( I have waited about 15 minutes, nothing happened)

Then I have also tried to flash unlocked version firmware and this time i have recieved ERROR 155 - IT says the device is not matching with firmware.

After that i have downloaded some apps from play store related to phone info search.

All these apps are suggesting that its a Sprint_WWE phone.

My phone does not have any logo on it or any bloat ware from the career.

I am confused now, which version of M8 i am using and which firmware RUU should i flash?

Please note: My Bootloader is in locked state and official recovery installed. Never rooted or CWM installed.
I am using this phone in Bangladesh right now so OTA is not coming to my phone.

 

[IAmSixNine]

I dont think there was an ATT Unlocked version. There is ATT and there is Unlocked.
You can unlock an ATT but thats now how it comes. My guess would be ATT but if theres no carrier bloat then maybe its the Unlocked version.