Perhaps You have several policies, where it is alowed in one of them. And You have to reorder them, in order to get it working.
But it is a funny restriction, voice calling is the most essential thing phones do
I have tried to restrict it on my iOS device.
It dosn't resctrict me from calling to my contacts by pressing one,
it dosn't resctrict med from calling to my contacts by using voice control,
it dosn't resctrict med from calling a new number.
Now I'm confused, what does it restrict???