Is_Page doesnt detect my page

Are you wanting to replace the template file for the entire page or include a certain feature? As @JacobPeattie mentioned in the comments you may want to check out template hierarchy for replacing the whole template.

The get_template_part() function can be used to include a template part into another file. I think that’s your use case here. The problem appears to be where you are trying to add the template. I think you’ll want to add the following to page.php as that is the default template for pages. I find that the Query Monitor plugin has a useful feature of displaying which template is being used.

 // add to page.php where you want your forms.
 if ( is_page( 'faq' ) || is_page( 'FAQ' ) ) {
        get_template_part( 'Servicedeneme' );
    }