It is dangerous to overfill a diesel engine with lubricating oil. If the level is too high, the oil can blow past the pistons, self fuelling the engine, you can't stop it, the revs increase until the engine blows up! That stops it!! I would get them to take out 2 litres, then put in again slowly until the MAX mark is reached. They probably didn't measure 4 - 4.5 litres or topped it up just after running the engine.