I know it has beena while since there was an update, but just in case anybody ever wonders “what happened with that guy and his wonky RAM?” The issue has been solved. After a deepdive into the internet to find the correct part number from HP, I only found it in the States (of course, as it is discontinued everywhere else). So after about a week of shipping to the UAE I just isntalled it and now my little experimental server is running at glorious 16 GB of RAM.
In the process of solving all of this, I discovered that the exact model that I have, used to ship with only 1x 8 GB module, so the guys that refurbished it changed it for what they thought was equivalent, but it was the wrong part number so It only recognized 1 of them.
Anyways, thank you very much for the help everyone!