I read somewhere that is written like that and I know this sentence is right.
Er lässt die Elektrofirma das System installieren. (He has the electro firm installed the system.)
But also, I saw somewhere else those two sentence below,
Ich lasse mir die Haare schneiden.
Ich lasse meinem Sohn die Haare schneiden
so my question is. in the first sentence die Elektrofirma is adjusted as Akkusative. Then why do we not do the same rule in other two sentence because they are dativ there. So I would say in the Akkusativ form.
Ich lasse mich die Haare schneiden.
Ich lasse meinen Sohn die Haare schneiden
So which sentences is right here ?