Plugin Form Processing hook content formating issue

Hello Devs, I am creating a plugin. But I stuck when processing the Form data using the hooks. The hook function xyz_view_mobile_form_submit() call of submenu giving the html content in whole webpage breaking the structure of wordpress. When the same html content is loaded in the submenu page content function xyz_fill_mobile_search() i.e. without hook function it shows as normal. The code is given below:

function xyz_dash_view_mobile(){
    $hookname = add_submenu_page( 
        'xyz_dash_option', //parent slug
        'xyz Dasboard View Mobile',// sub menu page <title>Title</title> 
    'View Mobile', // sub menu link text
    'manage_options', // capability to access the page
    'xyz_view_mobile', // page URL slug
     'nyag_fill_mobile_search', // callback function to show page content
     'dashicons-star-half', // menu icon
     3 // priority
     );
     add_action( 'load-' . $hookname, 'xyz_view_mobile_form_submit' );
}
//now Register submenu to Main Menu
add_action('admin_menu', 'xyz_dash_view_mobile');
//hooked function to process form data 
function xyz_view_mobile_form_submit()
{
    include_once( 's_mob_view.php' ); //This function content causing issue
}
//To Show Fill Data Page
function xyz_fill_mobile_search()
{      
    include_once( 'm_search.php' ); //include as php/html data file
}

P.S.- I am Newbie in wordpress Devlopment, Sorry if I forgot to explain clearly. Let me know if any problem in question ??