Have you checked the oil level yourself, don't trust the mechanic's word. First step go outside and check the oil level. What type of oil did you use for the top up and what oil did your local garage use?
You have an XH Commander made in Belgium just like the Aussie ones, (same, same) You should be using a Fully Synthetic 5W-30 oil that is compatible for cars with Diesel Particular Filters (DPF). Any old diesel oils will stuff your high tech diesel up. It's all in the manual.
XH V6 3 liter diesel Commander: R/H steer, 2 1/2"OME rear lift, 3" front lift - Murchinson coils with steel spacers on top of struts, JeepinByAl upper control arms, Bilsien shocks, GDE chip, Custom low profile transmission cross member, Black alloys, 32 1/2" rubber , Provent crank case filter, custom rockrails, Custom rear bar, Custom front bar with driving lights, custom front bash plate, 12000lb recovery winch, aftermarket CD/Nav/DVD/Rear Cam system, Interior LEDs, HID lights