Sudden high oil consumption in the V6 TDI?

Hello in the round, on 15.08. a service with oil change was made with my Diva. After I had picked up the car there, I checked at home whether the oil level is ok and it was probably also. Now I have the car because of another thing in the same workshop and this called me yesterday to tell me that about 3/4 liters of oil would be missing and whether they should fill this up. I was quite surprised and told them that they could do that, but not at my expense because the car was there for inspection a few days ago. They agreed with that. What I am surprised, however, is where the oil went? I did not drive 1000 km with the car in the meantime. Furthermore, it has never used oil before (it is regularly checked). Oil changes are always made every year. He has not excruciated or sunken unusually the last days (at least I or anyone else noticed) Can it vo n now come to immediately increased oil consumption and if so, what is the cause of it? Or am I worried for nothing? MfG MXPhaeton