Solution:
For some reason I had to stop mysqld and apache in order to renew the certificates. In fact, certbot tells you the ID of the process that has taken the port, so I kill the two process by using their ID and then I ran:
sudo certbot --authenticator standalone --installer apache --cert-name vanguardmagic.com -d vanguardmagic.com -d www.vanguardmagic.com
That solved the issue.
Thank you @sahsanu for the guidance!