Your CSC code...
Shows OXM = non regional (to be expected)
BTU = Samsung stock U.K. non-carrier branded
EUX = European non country specific
LUX = Luxembourg stock Samsung non-carrier branded, country specific. Very strange.
Normally, I would expect say, OXM and either BTU or LUX., depending on your SIM. This CSC code configuration would appear to be preventing your device from receiving updates.
Try the following steps...
If the above does not solve your issue, you will need to refer it to a Samsung Service centre.