Don’t you have a user to access the machine other than one of those used in Hestia? Or access with the root user? It’s possible that your hosting provider offers terminal access from its control panel.
If you can navigate to /usr/local/hestia/data/users/HESTIAUSERIDHERE (example admin or hestia) & be able to edit the user.conf file, then towards the end, you should be able to see these 2 lines:
LOGIN_USE_IPLIST='no'
LOGIN_ALLOW_IPS=''
First one’s value should be 'no and the second one should be blank.
Reboot the system or restart the firewall to get it working.