Host disables mail() function on your shared server?
Install PHPMailer & update all of your forms
https://www.inmotionhosting.com/support/website/using-phpmailer-to-send-mail-through-php/
https://help.dreamhost.com/hc/en-us/articles/360031174411-PHPMailer-Installing-on-a-shared-server
set debug to 0 so it does not show in your browser
Add your variables at the top and place your html for the email recipient in the body tag
And add the html for the thank you page at the bottom