Sadly this is why I gave up on a brand new Tiguan and found an EU5 SQ5 TDI. Two years of AdBlue trouble, starting with similar symptoms. The fill calibration is off, which requires dealer attention sadly. I did exactly the same, 10 litres and no change to the message "600 miles until no start". The "no start" scenario is ridiculous (and unnecessary). Mercedes owners can simply reset this on the dash.