Stand-alone heating starts on its own

Hello together! Despite the fact that I do not open double or triple threads on this topic! If yes, sorry for it! My problem: Have a Phaeton V6 Diesel year 06!2010! Very often it happens that after a ride and subsequent parking of the vehicle somehow seems to be getting the heater. I get out of the vehicle and then you can hear the heater starting like a turbine. Also it often smells like the typical Die This would not be so bad if I did not have the feeling that the consumption of the board computer unfortunately does not correspond to the consumption of the tank. It is a good one litre above the computer consumption. The extra consumption would be explained by the almost constant start of the stand heating when the vehicle is switched off! Has someone already had similar problem with the stand heating or an idea about it. Thank you already for your comments!