Because “contact” is the preset slug, the solution is go to your theme folder /wp-content/themes/oldcar/
Find page-contact.php file, just rename it to page-contact-template.php
Then, “contact” slug will be available to use.
What’s the current version of your theme? Is it the latest version?
Is it possible to tell me your link and login details with private reply that I can check it in backend?