Fix old opencart site

Hi, I have an old Opencart site built in 2012 - It was running fine until Siteground took it down due to Malware. I removed the Malware but now it wont go back up.

I need it fixing so it runs again.

Error:

[17-Jul-2024 14:10:23 UTC] PHP Fatal error: Uncaught Error: Call to undefined function mcrypt_create_iv() in /home/customer/www/...co.uk/public_html/system/library/encryption.php:8
Stack trace:
#0 /home/customer/www/...co.uk/public_html/index.php(218): Encryption->__construct('d40465268b90216...')
#1 {main}
thrown in /home/customer/www/....co.uk/public_html/system/library/encryption.php on line 8