Software Problems

I'm from United Kingdom and I have a LG G3 D855 - made in Korea and basically what's happen to my phone is I restarted it and it ended up in a firmware mode and everytime I take battery out and put it back in it sends me to that firmware mode so I gave the phone to the shop to have a look and he says the whole software of the phone has been wiped off, I tried to flash it using your method if my phone gets messed up or something but everytime it would get stuck after 10% so I handed the phone to the shop and basically he put a software on and it says V10J-GLOBAL-SI. But before my phone went messed up it was something like V20I-EURR-XX, I've been searching for files so I could try and get my phone software back but I don't know how too, I heard of 'KDZ' but what is the difference between tot file and a kdz and will the Europe kdz get my phone software back to normal or any method that you know that will get in back,
please reply I've been proper stressed.