Encoding matter – ? instead of € after settings field callback

In my plugin I have som classes to manage settings field.

For some reason in one moment the setting field value with special characters like 30€ in textarea or input[type=text] change to be 30?.

I got the value like this in my class :

And before to add settings fields, the text is correctly encoded.

For the callback, for some reasons, I´m using the magic method __call ( string $name , array $arguments ) :

So to get an overview to help a little more :

So, after the callback, there is a difference of encoding…

How can I resolve this ?