Please ignore last reply,
I have successfully debranded and unlocked my w850i , It took some time to do but i got there in the end.
But i think some instructions on here were not clear for me , so i did it this way>>
(first back up gdfs)
1. download 3 files fs,main,custom, make sure they all match language version etc
2. Flash with setool2lite v1.10 (update to v1.11 has trojan horse virus czs in the exe file)
3. Make vkp patch with above main file in simlock-patch generator4.
4. Add main file to setool2lite v1.10 in (ADD) section and vkp patch in (MISC ...) section
5. Tick the "bypass security DB2020" check box in setool2lite v1.10 . Select your phone model.
6. press FLASH button in setool2lite v1.10 (this also writes the vkp script) so no need to press WRITE SCRIPT button.
7.After some 10 mins or so click the pop up window NO to apply patch.
8.Bite your nails and hope for the best.
9.Insert a sim, turn on phone, wait for a few mins, then think to yourself how clever you are that you just unlocked and debranded your phone.

This is just a simple very rough guide on how i did it. thanks to all the info on this forum which gave me the confidence to do it.