My Miele fridge doesn't hold on to warmth and I inevitability to keep hold of pressing the "Super" button? I have a Miele K2214S fridge and it does not hang on...

I have a Miele K2214S fridge and it does not hang on to the temperature. It is on the lowest setting. If I press the "Super" button it chills down to the required warmth, but then it does not preserve it so. If I don't go final in a few hours to press "Super" again, the heat inside goes up and food go bad. Can you please suggest what may be wrong beside it and what I can do, apart from calling an engineer from the company (their charge is almost as much as the fridge is worth!). I involve to keep baby's milk within the fridge without worrying that the fridge may enjoy stopped working in the middle of the dark - please help.
Filling a cranny within the wall.?
Answers:    Pull fridge away from wall, verbs the coils on the back. Vacuum over ALL parts surrounded by back & underneath (dust may be clogging the working parts).
If own freezer portion of fridge as well as fridge, sort sure nothing is setting too close to the inside 'vent'.
Still a problem, sorry, it is any repair man or replace (it may be only low on freeon - - which cannot be done lacking being certified for it).