How can I stop continuous failed logins on SQL Server
It sounds like those failed logins are coming from the Internet.

You really shouldn't have a firewall port open to SQL Server directly from the Internet.  That is just asking for trouble.

If the website and SQL Server are not on the same network, or are connected only via the Internet, you should look at providing a VPN connection between the two so that you don't provide an open port directly from the Internet to SQL Server.