Hopefully i can help..
It does sound like you may have whats termed as a parasitic battery drain ie:- a component within the car drawing current from the battery whilst the ignitions off..
It might be worth checking once the battery is re-charged or the car jump started to double check the alternator is charging properly ie:- as an average around roughly 14.5v also from the output terminal on the alternator - and too check all earth points are clean and tight same with the terminals on the battery/alternator/starter etc - also too there is a chance the battery itself may not be holding a charge and thus may need replaced any garage can check the battery state to confrim that,if over 5 years old which some batteries do tend to this once they get older then can cause this sort of problem espeically being a diesel which has more demand on the battery for glowplugs/cold starting etc..
If there is drain on the battery - When cars ignitions off - also check for any and all exterior lights "including number plate lights which are always missed out" and interior lamps , glove box "if any"/ boot lights are not still on when the cars not in use or locked or any other item plugged in make sure it disconnected also check for any aftermarket fitted accessories are properly wired in..The only other test that can be done usually - is you will need to be checking the electrical draw the battery has on it when the car is locked up, with the key in the "off" position". and the doors locked wait 15 minutes roughly, then disconnect the battery cable on the negative/earth side. Attach a test light/ digital multimeter between the negative battery cable end and the negative battery terminal. The test light should illuminate extremely dimly or not at all. If the test light is on brightly or quite bright there is a sign there is an electrical draw in the system. To locate you will need to start removing fuses "one" at a time so you'll need to be carefull which ones you pull so you'll need to refer to the manual each time or the lid and start of with the know ones first in particular as far as the fuse(s) for those bulbs/lights. When the test light goes out or voltage drops on multimeter the circuit in question has been located . You will need to identify the pulled fuse and what it covers within the car and that should be where the parasitic drain is on that circuit either a faulty component/bulb holder or a wiring fault on that particular circuit which will need tracing and investigated..However if you don't have the proper test equipment - then i'm sure or at least any good reputable auto electrician "some of who maybe mobile" or garage with their equipment should be able to route it out in a similar way.so those are about the usual steps you can take as as a starting point anyway...I do hope this helps